1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Budget Fair Queueing (BFQ) I/O scheduler.
4 *
5 * Based on ideas and code from CFQ:
6 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 *
8 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
9 * Paolo Valente <paolo.valente@unimore.it>
10 *
11 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
12 * Arianna Avanzini <avanzini@google.com>
13 *
14 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15 *
16 * BFQ is a proportional-share I/O scheduler, with some extra
17 * low-latency capabilities. BFQ also supports full hierarchical
18 * scheduling through cgroups. Next paragraphs provide an introduction
19 * on BFQ inner workings. Details on BFQ benefits, usage and
20 * limitations can be found in Documentation/block/bfq-iosched.rst.
21 *
22 * BFQ is a proportional-share storage-I/O scheduling algorithm based
23 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
24 * budgets, measured in number of sectors, to processes instead of
25 * time slices. The device is not granted to the in-service process
26 * for a given time slice, but until it has exhausted its assigned
27 * budget. This change from the time to the service domain enables BFQ
28 * to distribute the device throughput among processes as desired,
29 * without any distortion due to throughput fluctuations, or to device
30 * internal queueing. BFQ uses an ad hoc internal scheduler, called
31 * B-WF2Q+, to schedule processes according to their budgets. More
32 * precisely, BFQ schedules queues associated with processes. Each
33 * process/queue is assigned a user-configurable weight, and B-WF2Q+
34 * guarantees that each queue receives a fraction of the throughput
35 * proportional to its weight. Thanks to the accurate policy of
36 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
37 * processes issuing sequential requests (to boost the throughput),
38 * and yet guarantee a low latency to interactive and soft real-time
39 * applications.
40 *
41 * In particular, to provide these low-latency guarantees, BFQ
42 * explicitly privileges the I/O of two classes of time-sensitive
43 * applications: interactive and soft real-time. In more detail, BFQ
44 * behaves this way if the low_latency parameter is set (default
45 * configuration). This feature enables BFQ to provide applications in
46 * these classes with a very low latency.
47 *
48 * To implement this feature, BFQ constantly tries to detect whether
49 * the I/O requests in a bfq_queue come from an interactive or a soft
50 * real-time application. For brevity, in these cases, the queue is
51 * said to be interactive or soft real-time. In both cases, BFQ
52 * privileges the service of the queue, over that of non-interactive
53 * and non-soft-real-time queues. This privileging is performed,
54 * mainly, by raising the weight of the queue. So, for brevity, we
55 * call just weight-raising periods the time periods during which a
56 * queue is privileged, because deemed interactive or soft real-time.
57 *
58 * The detection of soft real-time queues/applications is described in
59 * detail in the comments on the function
60 * bfq_bfqq_softrt_next_start. On the other hand, the detection of an
61 * interactive queue works as follows: a queue is deemed interactive
62 * if it is constantly non empty only for a limited time interval,
63 * after which it does become empty. The queue may be deemed
64 * interactive again (for a limited time), if it restarts being
65 * constantly non empty, provided that this happens only after the
66 * queue has remained empty for a given minimum idle time.
67 *
68 * By default, BFQ computes automatically the above maximum time
69 * interval, i.e., the time interval after which a constantly
70 * non-empty queue stops being deemed interactive. Since a queue is
71 * weight-raised while it is deemed interactive, this maximum time
72 * interval happens to coincide with the (maximum) duration of the
73 * weight-raising for interactive queues.
74 *
75 * Finally, BFQ also features additional heuristics for
76 * preserving both a low latency and a high throughput on NCQ-capable,
77 * rotational or flash-based devices, and to get the job done quickly
78 * for applications consisting in many I/O-bound processes.
79 *
80 * NOTE: if the main or only goal, with a given device, is to achieve
81 * the maximum-possible throughput at all times, then do switch off
82 * all low-latency heuristics for that device, by setting low_latency
83 * to 0.
84 *
85 * BFQ is described in [1], where also a reference to the initial,
86 * more theoretical paper on BFQ can be found. The interested reader
87 * can find in the latter paper full details on the main algorithm, as
88 * well as formulas of the guarantees and formal proofs of all the
89 * properties. With respect to the version of BFQ presented in these
90 * papers, this implementation adds a few more heuristics, such as the
91 * ones that guarantee a low latency to interactive and soft real-time
92 * applications, and a hierarchical extension based on H-WF2Q+.
93 *
94 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
95 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
96 * with O(log N) complexity derives from the one introduced with EEVDF
97 * in [3].
98 *
99 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
100 * Scheduler", Proceedings of the First Workshop on Mobile System
101 * Technologies (MST-2015), May 2015.
102 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
103 *
104 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
105 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
106 * Oct 1997.
107 *
108 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
109 *
110 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
111 * First: A Flexible and Accurate Mechanism for Proportional Share
112 * Resource Allocation", technical report.
113 *
114 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
115 */
116 #include <linux/module.h>
117 #include <linux/slab.h>
118 #include <linux/blkdev.h>
119 #include <linux/cgroup.h>
120 #include <linux/ktime.h>
121 #include <linux/rbtree.h>
122 #include <linux/ioprio.h>
123 #include <linux/sbitmap.h>
124 #include <linux/delay.h>
125 #include <linux/backing-dev.h>
126
127 #include <trace/events/block.h>
128
129 #include "elevator.h"
130 #include "blk.h"
131 #include "blk-mq.h"
132 #include "blk-mq-tag.h"
133 #include "blk-mq-sched.h"
134 #include "bfq-iosched.h"
135 #include "blk-wbt.h"
136
137 #define BFQ_BFQQ_FNS(name) \
138 void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
139 { \
140 __set_bit(BFQQF_##name, &(bfqq)->flags); \
141 } \
142 void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
143 { \
144 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
145 } \
146 int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
147 { \
148 return test_bit(BFQQF_##name, &(bfqq)->flags); \
149 }
150
151 BFQ_BFQQ_FNS(just_created);
152 BFQ_BFQQ_FNS(busy);
153 BFQ_BFQQ_FNS(wait_request);
154 BFQ_BFQQ_FNS(non_blocking_wait_rq);
155 BFQ_BFQQ_FNS(fifo_expire);
156 BFQ_BFQQ_FNS(has_short_ttime);
157 BFQ_BFQQ_FNS(sync);
158 BFQ_BFQQ_FNS(IO_bound);
159 BFQ_BFQQ_FNS(in_large_burst);
160 BFQ_BFQQ_FNS(coop);
161 BFQ_BFQQ_FNS(split_coop);
162 BFQ_BFQQ_FNS(softrt_update);
163 #undef BFQ_BFQQ_FNS \
164
165 /* Expiration time of async (0) and sync (1) requests, in ns. */
166 static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
167
168 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
169 static const int bfq_back_max = 16 * 1024;
170
171 /* Penalty of a backwards seek, in number of sectors. */
172 static const int bfq_back_penalty = 2;
173
174 /* Idling period duration, in ns. */
175 static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
176
177 /* Minimum number of assigned budgets for which stats are safe to compute. */
178 static const int bfq_stats_min_budgets = 194;
179
180 /* Default maximum budget values, in sectors and number of requests. */
181 static const int bfq_default_max_budget = 16 * 1024;
182
183 /*
184 * When a sync request is dispatched, the queue that contains that
185 * request, and all the ancestor entities of that queue, are charged
186 * with the number of sectors of the request. In contrast, if the
187 * request is async, then the queue and its ancestor entities are
188 * charged with the number of sectors of the request, multiplied by
189 * the factor below. This throttles the bandwidth for async I/O,
190 * w.r.t. to sync I/O, and it is done to counter the tendency of async
191 * writes to steal I/O throughput to reads.
192 *
193 * The current value of this parameter is the result of a tuning with
194 * several hardware and software configurations. We tried to find the
195 * lowest value for which writes do not cause noticeable problems to
196 * reads. In fact, the lower this parameter, the stabler I/O control,
197 * in the following respect. The lower this parameter is, the less
198 * the bandwidth enjoyed by a group decreases
199 * - when the group does writes, w.r.t. to when it does reads;
200 * - when other groups do reads, w.r.t. to when they do writes.
201 */
202 static const int bfq_async_charge_factor = 3;
203
204 /* Default timeout values, in jiffies, approximating CFQ defaults. */
205 const int bfq_timeout = HZ / 8;
206
207 /*
208 * Time limit for merging (see comments in bfq_setup_cooperator). Set
209 * to the slowest value that, in our tests, proved to be effective in
210 * removing false positives, while not causing true positives to miss
211 * queue merging.
212 *
213 * As can be deduced from the low time limit below, queue merging, if
214 * successful, happens at the very beginning of the I/O of the involved
215 * cooperating processes, as a consequence of the arrival of the very
216 * first requests from each cooperator. After that, there is very
217 * little chance to find cooperators.
218 */
219 static const unsigned long bfq_merge_time_limit = HZ/10;
220
221 static struct kmem_cache *bfq_pool;
222
223 /* Below this threshold (in ns), we consider thinktime immediate. */
224 #define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
225
226 /* hw_tag detection: parallel requests threshold and min samples needed. */
227 #define BFQ_HW_QUEUE_THRESHOLD 3
228 #define BFQ_HW_QUEUE_SAMPLES 32
229
230 #define BFQQ_SEEK_THR (sector_t)(8 * 100)
231 #define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
232 #define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
233 (get_sdist(last_pos, rq) > \
234 BFQQ_SEEK_THR && \
235 (!blk_queue_nonrot(bfqd->queue) || \
236 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
237 #define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
238 #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19)
239 /*
240 * Sync random I/O is likely to be confused with soft real-time I/O,
241 * because it is characterized by limited throughput and apparently
242 * isochronous arrival pattern. To avoid false positives, queues
243 * containing only random (seeky) I/O are prevented from being tagged
244 * as soft real-time.
245 */
246 #define BFQQ_TOTALLY_SEEKY(bfqq) (bfqq->seek_history == -1)
247
248 /* Min number of samples required to perform peak-rate update */
249 #define BFQ_RATE_MIN_SAMPLES 32
250 /* Min observation time interval required to perform a peak-rate update (ns) */
251 #define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
252 /* Target observation time interval for a peak-rate update (ns) */
253 #define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
254
255 /*
256 * Shift used for peak-rate fixed precision calculations.
257 * With
258 * - the current shift: 16 positions
259 * - the current type used to store rate: u32
260 * - the current unit of measure for rate: [sectors/usec], or, more precisely,
261 * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
262 * the range of rates that can be stored is
263 * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
264 * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
265 * [15, 65G] sectors/sec
266 * Which, assuming a sector size of 512B, corresponds to a range of
267 * [7.5K, 33T] B/sec
268 */
269 #define BFQ_RATE_SHIFT 16
270
271 /*
272 * When configured for computing the duration of the weight-raising
273 * for interactive queues automatically (see the comments at the
274 * beginning of this file), BFQ does it using the following formula:
275 * duration = (ref_rate / r) * ref_wr_duration,
276 * where r is the peak rate of the device, and ref_rate and
277 * ref_wr_duration are two reference parameters. In particular,
278 * ref_rate is the peak rate of the reference storage device (see
279 * below), and ref_wr_duration is about the maximum time needed, with
280 * BFQ and while reading two files in parallel, to load typical large
281 * applications on the reference device (see the comments on
282 * max_service_from_wr below, for more details on how ref_wr_duration
283 * is obtained). In practice, the slower/faster the device at hand
284 * is, the more/less it takes to load applications with respect to the
285 * reference device. Accordingly, the longer/shorter BFQ grants
286 * weight raising to interactive applications.
287 *
288 * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
289 * depending on whether the device is rotational or non-rotational.
290 *
291 * In the following definitions, ref_rate[0] and ref_wr_duration[0]
292 * are the reference values for a rotational device, whereas
293 * ref_rate[1] and ref_wr_duration[1] are the reference values for a
294 * non-rotational device. The reference rates are not the actual peak
295 * rates of the devices used as a reference, but slightly lower
296 * values. The reason for using slightly lower values is that the
297 * peak-rate estimator tends to yield slightly lower values than the
298 * actual peak rate (it can yield the actual peak rate only if there
299 * is only one process doing I/O, and the process does sequential
300 * I/O).
301 *
302 * The reference peak rates are measured in sectors/usec, left-shifted
303 * by BFQ_RATE_SHIFT.
304 */
305 static int ref_rate[2] = {14000, 33000};
306 /*
307 * To improve readability, a conversion function is used to initialize
308 * the following array, which entails that the array can be
309 * initialized only in a function.
310 */
311 static int ref_wr_duration[2];
312
313 /*
314 * BFQ uses the above-detailed, time-based weight-raising mechanism to
315 * privilege interactive tasks. This mechanism is vulnerable to the
316 * following false positives: I/O-bound applications that will go on
317 * doing I/O for much longer than the duration of weight
318 * raising. These applications have basically no benefit from being
319 * weight-raised at the beginning of their I/O. On the opposite end,
320 * while being weight-raised, these applications
321 * a) unjustly steal throughput to applications that may actually need
322 * low latency;
323 * b) make BFQ uselessly perform device idling; device idling results
324 * in loss of device throughput with most flash-based storage, and may
325 * increase latencies when used purposelessly.
326 *
327 * BFQ tries to reduce these problems, by adopting the following
328 * countermeasure. To introduce this countermeasure, we need first to
329 * finish explaining how the duration of weight-raising for
330 * interactive tasks is computed.
331 *
332 * For a bfq_queue deemed as interactive, the duration of weight
333 * raising is dynamically adjusted, as a function of the estimated
334 * peak rate of the device, so as to be equal to the time needed to
335 * execute the 'largest' interactive task we benchmarked so far. By
336 * largest task, we mean the task for which each involved process has
337 * to do more I/O than for any of the other tasks we benchmarked. This
338 * reference interactive task is the start-up of LibreOffice Writer,
339 * and in this task each process/bfq_queue needs to have at most ~110K
340 * sectors transferred.
341 *
342 * This last piece of information enables BFQ to reduce the actual
343 * duration of weight-raising for at least one class of I/O-bound
344 * applications: those doing sequential or quasi-sequential I/O. An
345 * example is file copy. In fact, once started, the main I/O-bound
346 * processes of these applications usually consume the above 110K
347 * sectors in much less time than the processes of an application that
348 * is starting, because these I/O-bound processes will greedily devote
349 * almost all their CPU cycles only to their target,
350 * throughput-friendly I/O operations. This is even more true if BFQ
351 * happens to be underestimating the device peak rate, and thus
352 * overestimating the duration of weight raising. But, according to
353 * our measurements, once transferred 110K sectors, these processes
354 * have no right to be weight-raised any longer.
355 *
356 * Basing on the last consideration, BFQ ends weight-raising for a
357 * bfq_queue if the latter happens to have received an amount of
358 * service at least equal to the following constant. The constant is
359 * set to slightly more than 110K, to have a minimum safety margin.
360 *
361 * This early ending of weight-raising reduces the amount of time
362 * during which interactive false positives cause the two problems
363 * described at the beginning of these comments.
364 */
365 static const unsigned long max_service_from_wr = 120000;
366
367 /*
368 * Maximum time between the creation of two queues, for stable merge
369 * to be activated (in ms)
370 */
371 static const unsigned long bfq_activation_stable_merging = 600;
372 /*
373 * Minimum time to be waited before evaluating delayed stable merge (in ms)
374 */
375 static const unsigned long bfq_late_stable_merging = 600;
376
377 #define RQ_BIC(rq) ((struct bfq_io_cq *)((rq)->elv.priv[0]))
378 #define RQ_BFQQ(rq) ((rq)->elv.priv[1])
379
bic_to_bfqq(struct bfq_io_cq * bic,bool is_sync)380 struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
381 {
382 return bic->bfqq[is_sync];
383 }
384
385 static void bfq_put_stable_ref(struct bfq_queue *bfqq);
386
bic_set_bfqq(struct bfq_io_cq * bic,struct bfq_queue * bfqq,bool is_sync)387 void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
388 {
389 struct bfq_queue *old_bfqq = bic->bfqq[is_sync];
390
391 /* Clear bic pointer if bfqq is detached from this bic */
392 if (old_bfqq && old_bfqq->bic == bic)
393 old_bfqq->bic = NULL;
394
395 /*
396 * If bfqq != NULL, then a non-stable queue merge between
397 * bic->bfqq and bfqq is happening here. This causes troubles
398 * in the following case: bic->bfqq has also been scheduled
399 * for a possible stable merge with bic->stable_merge_bfqq,
400 * and bic->stable_merge_bfqq == bfqq happens to
401 * hold. Troubles occur because bfqq may then undergo a split,
402 * thereby becoming eligible for a stable merge. Yet, if
403 * bic->stable_merge_bfqq points exactly to bfqq, then bfqq
404 * would be stably merged with itself. To avoid this anomaly,
405 * we cancel the stable merge if
406 * bic->stable_merge_bfqq == bfqq.
407 */
408 bic->bfqq[is_sync] = bfqq;
409
410 if (bfqq && bic->stable_merge_bfqq == bfqq) {
411 /*
412 * Actually, these same instructions are executed also
413 * in bfq_setup_cooperator, in case of abort or actual
414 * execution of a stable merge. We could avoid
415 * repeating these instructions there too, but if we
416 * did so, we would nest even more complexity in this
417 * function.
418 */
419 bfq_put_stable_ref(bic->stable_merge_bfqq);
420
421 bic->stable_merge_bfqq = NULL;
422 }
423 }
424
bic_to_bfqd(struct bfq_io_cq * bic)425 struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
426 {
427 return bic->icq.q->elevator->elevator_data;
428 }
429
430 /**
431 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
432 * @icq: the iocontext queue.
433 */
icq_to_bic(struct io_cq * icq)434 static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
435 {
436 /* bic->icq is the first member, %NULL will convert to %NULL */
437 return container_of(icq, struct bfq_io_cq, icq);
438 }
439
440 /**
441 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
442 * @q: the request queue.
443 */
bfq_bic_lookup(struct request_queue * q)444 static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q)
445 {
446 struct bfq_io_cq *icq;
447 unsigned long flags;
448
449 if (!current->io_context)
450 return NULL;
451
452 spin_lock_irqsave(&q->queue_lock, flags);
453 icq = icq_to_bic(ioc_lookup_icq(q));
454 spin_unlock_irqrestore(&q->queue_lock, flags);
455
456 return icq;
457 }
458
459 /*
460 * Scheduler run of queue, if there are requests pending and no one in the
461 * driver that will restart queueing.
462 */
bfq_schedule_dispatch(struct bfq_data * bfqd)463 void bfq_schedule_dispatch(struct bfq_data *bfqd)
464 {
465 lockdep_assert_held(&bfqd->lock);
466
467 if (bfqd->queued != 0) {
468 bfq_log(bfqd, "schedule dispatch");
469 blk_mq_run_hw_queues(bfqd->queue, true);
470 }
471 }
472
473 #define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
474
475 #define bfq_sample_valid(samples) ((samples) > 80)
476
477 /*
478 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
479 * We choose the request that is closer to the head right now. Distance
480 * behind the head is penalized and only allowed to a certain extent.
481 */
bfq_choose_req(struct bfq_data * bfqd,struct request * rq1,struct request * rq2,sector_t last)482 static struct request *bfq_choose_req(struct bfq_data *bfqd,
483 struct request *rq1,
484 struct request *rq2,
485 sector_t last)
486 {
487 sector_t s1, s2, d1 = 0, d2 = 0;
488 unsigned long back_max;
489 #define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
490 #define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
491 unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
492
493 if (!rq1 || rq1 == rq2)
494 return rq2;
495 if (!rq2)
496 return rq1;
497
498 if (rq_is_sync(rq1) && !rq_is_sync(rq2))
499 return rq1;
500 else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
501 return rq2;
502 if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
503 return rq1;
504 else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
505 return rq2;
506
507 s1 = blk_rq_pos(rq1);
508 s2 = blk_rq_pos(rq2);
509
510 /*
511 * By definition, 1KiB is 2 sectors.
512 */
513 back_max = bfqd->bfq_back_max * 2;
514
515 /*
516 * Strict one way elevator _except_ in the case where we allow
517 * short backward seeks which are biased as twice the cost of a
518 * similar forward seek.
519 */
520 if (s1 >= last)
521 d1 = s1 - last;
522 else if (s1 + back_max >= last)
523 d1 = (last - s1) * bfqd->bfq_back_penalty;
524 else
525 wrap |= BFQ_RQ1_WRAP;
526
527 if (s2 >= last)
528 d2 = s2 - last;
529 else if (s2 + back_max >= last)
530 d2 = (last - s2) * bfqd->bfq_back_penalty;
531 else
532 wrap |= BFQ_RQ2_WRAP;
533
534 /* Found required data */
535
536 /*
537 * By doing switch() on the bit mask "wrap" we avoid having to
538 * check two variables for all permutations: --> faster!
539 */
540 switch (wrap) {
541 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
542 if (d1 < d2)
543 return rq1;
544 else if (d2 < d1)
545 return rq2;
546
547 if (s1 >= s2)
548 return rq1;
549 else
550 return rq2;
551
552 case BFQ_RQ2_WRAP:
553 return rq1;
554 case BFQ_RQ1_WRAP:
555 return rq2;
556 case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
557 default:
558 /*
559 * Since both rqs are wrapped,
560 * start with the one that's further behind head
561 * (--> only *one* back seek required),
562 * since back seek takes more time than forward.
563 */
564 if (s1 <= s2)
565 return rq1;
566 else
567 return rq2;
568 }
569 }
570
571 #define BFQ_LIMIT_INLINE_DEPTH 16
572
573 #ifdef CONFIG_BFQ_GROUP_IOSCHED
bfqq_request_over_limit(struct bfq_queue * bfqq,int limit)574 static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
575 {
576 struct bfq_data *bfqd = bfqq->bfqd;
577 struct bfq_entity *entity = &bfqq->entity;
578 struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
579 struct bfq_entity **entities = inline_entities;
580 int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
581 int class_idx = bfqq->ioprio_class - 1;
582 struct bfq_sched_data *sched_data;
583 unsigned long wsum;
584 bool ret = false;
585
586 if (!entity->on_st_or_in_serv)
587 return false;
588
589 retry:
590 spin_lock_irq(&bfqd->lock);
591 /* +1 for bfqq entity, root cgroup not included */
592 depth = bfqg_to_blkg(bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
593 if (depth > alloc_depth) {
594 spin_unlock_irq(&bfqd->lock);
595 if (entities != inline_entities)
596 kfree(entities);
597 entities = kmalloc_array(depth, sizeof(*entities), GFP_NOIO);
598 if (!entities)
599 return false;
600 alloc_depth = depth;
601 goto retry;
602 }
603
604 sched_data = entity->sched_data;
605 /* Gather our ancestors as we need to traverse them in reverse order */
606 level = 0;
607 for_each_entity(entity) {
608 /*
609 * If at some level entity is not even active, allow request
610 * queueing so that BFQ knows there's work to do and activate
611 * entities.
612 */
613 if (!entity->on_st_or_in_serv)
614 goto out;
615 /* Uh, more parents than cgroup subsystem thinks? */
616 if (WARN_ON_ONCE(level >= depth))
617 break;
618 entities[level++] = entity;
619 }
620 WARN_ON_ONCE(level != depth);
621 for (level--; level >= 0; level--) {
622 entity = entities[level];
623 if (level > 0) {
624 wsum = bfq_entity_service_tree(entity)->wsum;
625 } else {
626 int i;
627 /*
628 * For bfqq itself we take into account service trees
629 * of all higher priority classes and multiply their
630 * weights so that low prio queue from higher class
631 * gets more requests than high prio queue from lower
632 * class.
633 */
634 wsum = 0;
635 for (i = 0; i <= class_idx; i++) {
636 wsum = wsum * IOPRIO_BE_NR +
637 sched_data->service_tree[i].wsum;
638 }
639 }
640 if (!wsum)
641 continue;
642 limit = DIV_ROUND_CLOSEST(limit * entity->weight, wsum);
643 if (entity->allocated >= limit) {
644 bfq_log_bfqq(bfqq->bfqd, bfqq,
645 "too many requests: allocated %d limit %d level %d",
646 entity->allocated, limit, level);
647 ret = true;
648 break;
649 }
650 }
651 out:
652 spin_unlock_irq(&bfqd->lock);
653 if (entities != inline_entities)
654 kfree(entities);
655 return ret;
656 }
657 #else
bfqq_request_over_limit(struct bfq_queue * bfqq,int limit)658 static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
659 {
660 return false;
661 }
662 #endif
663
664 /*
665 * Async I/O can easily starve sync I/O (both sync reads and sync
666 * writes), by consuming all tags. Similarly, storms of sync writes,
667 * such as those that sync(2) may trigger, can starve sync reads.
668 * Limit depths of async I/O and sync writes so as to counter both
669 * problems.
670 *
671 * Also if a bfq queue or its parent cgroup consume more tags than would be
672 * appropriate for their weight, we trim the available tag depth to 1. This
673 * avoids a situation where one cgroup can starve another cgroup from tags and
674 * thus block service differentiation among cgroups. Note that because the
675 * queue / cgroup already has many requests allocated and queued, this does not
676 * significantly affect service guarantees coming from the BFQ scheduling
677 * algorithm.
678 */
bfq_limit_depth(blk_opf_t opf,struct blk_mq_alloc_data * data)679 static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
680 {
681 struct bfq_data *bfqd = data->q->elevator->elevator_data;
682 struct bfq_io_cq *bic = bfq_bic_lookup(data->q);
683 struct bfq_queue *bfqq = bic ? bic_to_bfqq(bic, op_is_sync(opf)) : NULL;
684 int depth;
685 unsigned limit = data->q->nr_requests;
686
687 /* Sync reads have full depth available */
688 if (op_is_sync(opf) && !op_is_write(opf)) {
689 depth = 0;
690 } else {
691 depth = bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(opf)];
692 limit = (limit * depth) >> bfqd->full_depth_shift;
693 }
694
695 /*
696 * Does queue (or any parent entity) exceed number of requests that
697 * should be available to it? Heavily limit depth so that it cannot
698 * consume more available requests and thus starve other entities.
699 */
700 if (bfqq && bfqq_request_over_limit(bfqq, limit))
701 depth = 1;
702
703 bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
704 __func__, bfqd->wr_busy_queues, op_is_sync(opf), depth);
705 if (depth)
706 data->shallow_depth = depth;
707 }
708
709 static struct bfq_queue *
bfq_rq_pos_tree_lookup(struct bfq_data * bfqd,struct rb_root * root,sector_t sector,struct rb_node ** ret_parent,struct rb_node *** rb_link)710 bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
711 sector_t sector, struct rb_node **ret_parent,
712 struct rb_node ***rb_link)
713 {
714 struct rb_node **p, *parent;
715 struct bfq_queue *bfqq = NULL;
716
717 parent = NULL;
718 p = &root->rb_node;
719 while (*p) {
720 struct rb_node **n;
721
722 parent = *p;
723 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
724
725 /*
726 * Sort strictly based on sector. Smallest to the left,
727 * largest to the right.
728 */
729 if (sector > blk_rq_pos(bfqq->next_rq))
730 n = &(*p)->rb_right;
731 else if (sector < blk_rq_pos(bfqq->next_rq))
732 n = &(*p)->rb_left;
733 else
734 break;
735 p = n;
736 bfqq = NULL;
737 }
738
739 *ret_parent = parent;
740 if (rb_link)
741 *rb_link = p;
742
743 bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
744 (unsigned long long)sector,
745 bfqq ? bfqq->pid : 0);
746
747 return bfqq;
748 }
749
bfq_too_late_for_merging(struct bfq_queue * bfqq)750 static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
751 {
752 return bfqq->service_from_backlogged > 0 &&
753 time_is_before_jiffies(bfqq->first_IO_time +
754 bfq_merge_time_limit);
755 }
756
757 /*
758 * The following function is not marked as __cold because it is
759 * actually cold, but for the same performance goal described in the
760 * comments on the likely() at the beginning of
761 * bfq_setup_cooperator(). Unexpectedly, to reach an even lower
762 * execution time for the case where this function is not invoked, we
763 * had to add an unlikely() in each involved if().
764 */
765 void __cold
bfq_pos_tree_add_move(struct bfq_data * bfqd,struct bfq_queue * bfqq)766 bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
767 {
768 struct rb_node **p, *parent;
769 struct bfq_queue *__bfqq;
770
771 if (bfqq->pos_root) {
772 rb_erase(&bfqq->pos_node, bfqq->pos_root);
773 bfqq->pos_root = NULL;
774 }
775
776 /* oom_bfqq does not participate in queue merging */
777 if (bfqq == &bfqd->oom_bfqq)
778 return;
779
780 /*
781 * bfqq cannot be merged any longer (see comments in
782 * bfq_setup_cooperator): no point in adding bfqq into the
783 * position tree.
784 */
785 if (bfq_too_late_for_merging(bfqq))
786 return;
787
788 if (bfq_class_idle(bfqq))
789 return;
790 if (!bfqq->next_rq)
791 return;
792
793 bfqq->pos_root = &bfqq_group(bfqq)->rq_pos_tree;
794 __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
795 blk_rq_pos(bfqq->next_rq), &parent, &p);
796 if (!__bfqq) {
797 rb_link_node(&bfqq->pos_node, parent, p);
798 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
799 } else
800 bfqq->pos_root = NULL;
801 }
802
803 /*
804 * The following function returns false either if every active queue
805 * must receive the same share of the throughput (symmetric scenario),
806 * or, as a special case, if bfqq must receive a share of the
807 * throughput lower than or equal to the share that every other active
808 * queue must receive. If bfqq does sync I/O, then these are the only
809 * two cases where bfqq happens to be guaranteed its share of the
810 * throughput even if I/O dispatching is not plugged when bfqq remains
811 * temporarily empty (for more details, see the comments in the
812 * function bfq_better_to_idle()). For this reason, the return value
813 * of this function is used to check whether I/O-dispatch plugging can
814 * be avoided.
815 *
816 * The above first case (symmetric scenario) occurs when:
817 * 1) all active queues have the same weight,
818 * 2) all active queues belong to the same I/O-priority class,
819 * 3) all active groups at the same level in the groups tree have the same
820 * weight,
821 * 4) all active groups at the same level in the groups tree have the same
822 * number of children.
823 *
824 * Unfortunately, keeping the necessary state for evaluating exactly
825 * the last two symmetry sub-conditions above would be quite complex
826 * and time consuming. Therefore this function evaluates, instead,
827 * only the following stronger three sub-conditions, for which it is
828 * much easier to maintain the needed state:
829 * 1) all active queues have the same weight,
830 * 2) all active queues belong to the same I/O-priority class,
831 * 3) there are no active groups.
832 * In particular, the last condition is always true if hierarchical
833 * support or the cgroups interface are not enabled, thus no state
834 * needs to be maintained in this case.
835 */
bfq_asymmetric_scenario(struct bfq_data * bfqd,struct bfq_queue * bfqq)836 static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
837 struct bfq_queue *bfqq)
838 {
839 bool smallest_weight = bfqq &&
840 bfqq->weight_counter &&
841 bfqq->weight_counter ==
842 container_of(
843 rb_first_cached(&bfqd->queue_weights_tree),
844 struct bfq_weight_counter,
845 weights_node);
846
847 /*
848 * For queue weights to differ, queue_weights_tree must contain
849 * at least two nodes.
850 */
851 bool varied_queue_weights = !smallest_weight &&
852 !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
853 (bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
854 bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
855
856 bool multiple_classes_busy =
857 (bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
858 (bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
859 (bfqd->busy_queues[1] && bfqd->busy_queues[2]);
860
861 return varied_queue_weights || multiple_classes_busy
862 #ifdef CONFIG_BFQ_GROUP_IOSCHED
863 || bfqd->num_groups_with_pending_reqs > 0
864 #endif
865 ;
866 }
867
868 /*
869 * If the weight-counter tree passed as input contains no counter for
870 * the weight of the input queue, then add that counter; otherwise just
871 * increment the existing counter.
872 *
873 * Note that weight-counter trees contain few nodes in mostly symmetric
874 * scenarios. For example, if all queues have the same weight, then the
875 * weight-counter tree for the queues may contain at most one node.
876 * This holds even if low_latency is on, because weight-raised queues
877 * are not inserted in the tree.
878 * In most scenarios, the rate at which nodes are created/destroyed
879 * should be low too.
880 */
bfq_weights_tree_add(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct rb_root_cached * root)881 void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
882 struct rb_root_cached *root)
883 {
884 struct bfq_entity *entity = &bfqq->entity;
885 struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
886 bool leftmost = true;
887
888 /*
889 * Do not insert if the queue is already associated with a
890 * counter, which happens if:
891 * 1) a request arrival has caused the queue to become both
892 * non-weight-raised, and hence change its weight, and
893 * backlogged; in this respect, each of the two events
894 * causes an invocation of this function,
895 * 2) this is the invocation of this function caused by the
896 * second event. This second invocation is actually useless,
897 * and we handle this fact by exiting immediately. More
898 * efficient or clearer solutions might possibly be adopted.
899 */
900 if (bfqq->weight_counter)
901 return;
902
903 while (*new) {
904 struct bfq_weight_counter *__counter = container_of(*new,
905 struct bfq_weight_counter,
906 weights_node);
907 parent = *new;
908
909 if (entity->weight == __counter->weight) {
910 bfqq->weight_counter = __counter;
911 goto inc_counter;
912 }
913 if (entity->weight < __counter->weight)
914 new = &((*new)->rb_left);
915 else {
916 new = &((*new)->rb_right);
917 leftmost = false;
918 }
919 }
920
921 bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
922 GFP_ATOMIC);
923
924 /*
925 * In the unlucky event of an allocation failure, we just
926 * exit. This will cause the weight of queue to not be
927 * considered in bfq_asymmetric_scenario, which, in its turn,
928 * causes the scenario to be deemed wrongly symmetric in case
929 * bfqq's weight would have been the only weight making the
930 * scenario asymmetric. On the bright side, no unbalance will
931 * however occur when bfqq becomes inactive again (the
932 * invocation of this function is triggered by an activation
933 * of queue). In fact, bfq_weights_tree_remove does nothing
934 * if !bfqq->weight_counter.
935 */
936 if (unlikely(!bfqq->weight_counter))
937 return;
938
939 bfqq->weight_counter->weight = entity->weight;
940 rb_link_node(&bfqq->weight_counter->weights_node, parent, new);
941 rb_insert_color_cached(&bfqq->weight_counter->weights_node, root,
942 leftmost);
943
944 inc_counter:
945 bfqq->weight_counter->num_active++;
946 bfqq->ref++;
947 }
948
949 /*
950 * Decrement the weight counter associated with the queue, and, if the
951 * counter reaches 0, remove the counter from the tree.
952 * See the comments to the function bfq_weights_tree_add() for considerations
953 * about overhead.
954 */
__bfq_weights_tree_remove(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct rb_root_cached * root)955 void __bfq_weights_tree_remove(struct bfq_data *bfqd,
956 struct bfq_queue *bfqq,
957 struct rb_root_cached *root)
958 {
959 if (!bfqq->weight_counter)
960 return;
961
962 bfqq->weight_counter->num_active--;
963 if (bfqq->weight_counter->num_active > 0)
964 goto reset_entity_pointer;
965
966 rb_erase_cached(&bfqq->weight_counter->weights_node, root);
967 kfree(bfqq->weight_counter);
968
969 reset_entity_pointer:
970 bfqq->weight_counter = NULL;
971 bfq_put_queue(bfqq);
972 }
973
974 /*
975 * Invoke __bfq_weights_tree_remove on bfqq and decrement the number
976 * of active groups for each queue's inactive parent entity.
977 */
bfq_weights_tree_remove(struct bfq_data * bfqd,struct bfq_queue * bfqq)978 void bfq_weights_tree_remove(struct bfq_data *bfqd,
979 struct bfq_queue *bfqq)
980 {
981 struct bfq_entity *entity = bfqq->entity.parent;
982
983 for_each_entity(entity) {
984 struct bfq_sched_data *sd = entity->my_sched_data;
985
986 if (sd->next_in_service || sd->in_service_entity) {
987 /*
988 * entity is still active, because either
989 * next_in_service or in_service_entity is not
990 * NULL (see the comments on the definition of
991 * next_in_service for details on why
992 * in_service_entity must be checked too).
993 *
994 * As a consequence, its parent entities are
995 * active as well, and thus this loop must
996 * stop here.
997 */
998 break;
999 }
1000
1001 /*
1002 * The decrement of num_groups_with_pending_reqs is
1003 * not performed immediately upon the deactivation of
1004 * entity, but it is delayed to when it also happens
1005 * that the first leaf descendant bfqq of entity gets
1006 * all its pending requests completed. The following
1007 * instructions perform this delayed decrement, if
1008 * needed. See the comments on
1009 * num_groups_with_pending_reqs for details.
1010 */
1011 if (entity->in_groups_with_pending_reqs) {
1012 entity->in_groups_with_pending_reqs = false;
1013 bfqd->num_groups_with_pending_reqs--;
1014 }
1015 }
1016
1017 /*
1018 * Next function is invoked last, because it causes bfqq to be
1019 * freed if the following holds: bfqq is not in service and
1020 * has no dispatched request. DO NOT use bfqq after the next
1021 * function invocation.
1022 */
1023 __bfq_weights_tree_remove(bfqd, bfqq,
1024 &bfqd->queue_weights_tree);
1025 }
1026
1027 /*
1028 * Return expired entry, or NULL to just start from scratch in rbtree.
1029 */
bfq_check_fifo(struct bfq_queue * bfqq,struct request * last)1030 static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
1031 struct request *last)
1032 {
1033 struct request *rq;
1034
1035 if (bfq_bfqq_fifo_expire(bfqq))
1036 return NULL;
1037
1038 bfq_mark_bfqq_fifo_expire(bfqq);
1039
1040 rq = rq_entry_fifo(bfqq->fifo.next);
1041
1042 if (rq == last || ktime_get_ns() < rq->fifo_time)
1043 return NULL;
1044
1045 bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
1046 return rq;
1047 }
1048
bfq_find_next_rq(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct request * last)1049 static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
1050 struct bfq_queue *bfqq,
1051 struct request *last)
1052 {
1053 struct rb_node *rbnext = rb_next(&last->rb_node);
1054 struct rb_node *rbprev = rb_prev(&last->rb_node);
1055 struct request *next, *prev = NULL;
1056
1057 /* Follow expired path, else get first next available. */
1058 next = bfq_check_fifo(bfqq, last);
1059 if (next)
1060 return next;
1061
1062 if (rbprev)
1063 prev = rb_entry_rq(rbprev);
1064
1065 if (rbnext)
1066 next = rb_entry_rq(rbnext);
1067 else {
1068 rbnext = rb_first(&bfqq->sort_list);
1069 if (rbnext && rbnext != &last->rb_node)
1070 next = rb_entry_rq(rbnext);
1071 }
1072
1073 return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
1074 }
1075
1076 /* see the definition of bfq_async_charge_factor for details */
bfq_serv_to_charge(struct request * rq,struct bfq_queue * bfqq)1077 static unsigned long bfq_serv_to_charge(struct request *rq,
1078 struct bfq_queue *bfqq)
1079 {
1080 if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
1081 bfq_asymmetric_scenario(bfqq->bfqd, bfqq))
1082 return blk_rq_sectors(rq);
1083
1084 return blk_rq_sectors(rq) * bfq_async_charge_factor;
1085 }
1086
1087 /**
1088 * bfq_updated_next_req - update the queue after a new next_rq selection.
1089 * @bfqd: the device data the queue belongs to.
1090 * @bfqq: the queue to update.
1091 *
1092 * If the first request of a queue changes we make sure that the queue
1093 * has enough budget to serve at least its first request (if the
1094 * request has grown). We do this because if the queue has not enough
1095 * budget for its first request, it has to go through two dispatch
1096 * rounds to actually get it dispatched.
1097 */
bfq_updated_next_req(struct bfq_data * bfqd,struct bfq_queue * bfqq)1098 static void bfq_updated_next_req(struct bfq_data *bfqd,
1099 struct bfq_queue *bfqq)
1100 {
1101 struct bfq_entity *entity = &bfqq->entity;
1102 struct request *next_rq = bfqq->next_rq;
1103 unsigned long new_budget;
1104
1105 if (!next_rq)
1106 return;
1107
1108 if (bfqq == bfqd->in_service_queue)
1109 /*
1110 * In order not to break guarantees, budgets cannot be
1111 * changed after an entity has been selected.
1112 */
1113 return;
1114
1115 new_budget = max_t(unsigned long,
1116 max_t(unsigned long, bfqq->max_budget,
1117 bfq_serv_to_charge(next_rq, bfqq)),
1118 entity->service);
1119 if (entity->budget != new_budget) {
1120 entity->budget = new_budget;
1121 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
1122 new_budget);
1123 bfq_requeue_bfqq(bfqd, bfqq, false);
1124 }
1125 }
1126
bfq_wr_duration(struct bfq_data * bfqd)1127 static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
1128 {
1129 u64 dur;
1130
1131 if (bfqd->bfq_wr_max_time > 0)
1132 return bfqd->bfq_wr_max_time;
1133
1134 dur = bfqd->rate_dur_prod;
1135 do_div(dur, bfqd->peak_rate);
1136
1137 /*
1138 * Limit duration between 3 and 25 seconds. The upper limit
1139 * has been conservatively set after the following worst case:
1140 * on a QEMU/KVM virtual machine
1141 * - running in a slow PC
1142 * - with a virtual disk stacked on a slow low-end 5400rpm HDD
1143 * - serving a heavy I/O workload, such as the sequential reading
1144 * of several files
1145 * mplayer took 23 seconds to start, if constantly weight-raised.
1146 *
1147 * As for higher values than that accommodating the above bad
1148 * scenario, tests show that higher values would often yield
1149 * the opposite of the desired result, i.e., would worsen
1150 * responsiveness by allowing non-interactive applications to
1151 * preserve weight raising for too long.
1152 *
1153 * On the other end, lower values than 3 seconds make it
1154 * difficult for most interactive tasks to complete their jobs
1155 * before weight-raising finishes.
1156 */
1157 return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
1158 }
1159
1160 /* switch back from soft real-time to interactive weight raising */
switch_back_to_interactive_wr(struct bfq_queue * bfqq,struct bfq_data * bfqd)1161 static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1162 struct bfq_data *bfqd)
1163 {
1164 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1165 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1166 bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1167 }
1168
1169 static void
bfq_bfqq_resume_state(struct bfq_queue * bfqq,struct bfq_data * bfqd,struct bfq_io_cq * bic,bool bfq_already_existing)1170 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1171 struct bfq_io_cq *bic, bool bfq_already_existing)
1172 {
1173 unsigned int old_wr_coeff = 1;
1174 bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1175
1176 if (bic->saved_has_short_ttime)
1177 bfq_mark_bfqq_has_short_ttime(bfqq);
1178 else
1179 bfq_clear_bfqq_has_short_ttime(bfqq);
1180
1181 if (bic->saved_IO_bound)
1182 bfq_mark_bfqq_IO_bound(bfqq);
1183 else
1184 bfq_clear_bfqq_IO_bound(bfqq);
1185
1186 bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns;
1187 bfqq->inject_limit = bic->saved_inject_limit;
1188 bfqq->decrease_time_jif = bic->saved_decrease_time_jif;
1189
1190 bfqq->entity.new_weight = bic->saved_weight;
1191 bfqq->ttime = bic->saved_ttime;
1192 bfqq->io_start_time = bic->saved_io_start_time;
1193 bfqq->tot_idle_time = bic->saved_tot_idle_time;
1194 /*
1195 * Restore weight coefficient only if low_latency is on
1196 */
1197 if (bfqd->low_latency) {
1198 old_wr_coeff = bfqq->wr_coeff;
1199 bfqq->wr_coeff = bic->saved_wr_coeff;
1200 }
1201 bfqq->service_from_wr = bic->saved_service_from_wr;
1202 bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
1203 bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
1204 bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
1205
1206 if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1207 time_is_before_jiffies(bfqq->last_wr_start_finish +
1208 bfqq->wr_cur_max_time))) {
1209 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1210 !bfq_bfqq_in_large_burst(bfqq) &&
1211 time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1212 bfq_wr_duration(bfqd))) {
1213 switch_back_to_interactive_wr(bfqq, bfqd);
1214 } else {
1215 bfqq->wr_coeff = 1;
1216 bfq_log_bfqq(bfqq->bfqd, bfqq,
1217 "resume state: switching off wr");
1218 }
1219 }
1220
1221 /* make sure weight will be updated, however we got here */
1222 bfqq->entity.prio_changed = 1;
1223
1224 if (likely(!busy))
1225 return;
1226
1227 if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1228 bfqd->wr_busy_queues++;
1229 else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1230 bfqd->wr_busy_queues--;
1231 }
1232
bfqq_process_refs(struct bfq_queue * bfqq)1233 static int bfqq_process_refs(struct bfq_queue *bfqq)
1234 {
1235 return bfqq->ref - bfqq->entity.allocated -
1236 bfqq->entity.on_st_or_in_serv -
1237 (bfqq->weight_counter != NULL) - bfqq->stable_ref;
1238 }
1239
1240 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
bfq_reset_burst_list(struct bfq_data * bfqd,struct bfq_queue * bfqq)1241 static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1242 {
1243 struct bfq_queue *item;
1244 struct hlist_node *n;
1245
1246 hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1247 hlist_del_init(&item->burst_list_node);
1248
1249 /*
1250 * Start the creation of a new burst list only if there is no
1251 * active queue. See comments on the conditional invocation of
1252 * bfq_handle_burst().
1253 */
1254 if (bfq_tot_busy_queues(bfqd) == 0) {
1255 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1256 bfqd->burst_size = 1;
1257 } else
1258 bfqd->burst_size = 0;
1259
1260 bfqd->burst_parent_entity = bfqq->entity.parent;
1261 }
1262
1263 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
bfq_add_to_burst(struct bfq_data * bfqd,struct bfq_queue * bfqq)1264 static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1265 {
1266 /* Increment burst size to take into account also bfqq */
1267 bfqd->burst_size++;
1268
1269 if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1270 struct bfq_queue *pos, *bfqq_item;
1271 struct hlist_node *n;
1272
1273 /*
1274 * Enough queues have been activated shortly after each
1275 * other to consider this burst as large.
1276 */
1277 bfqd->large_burst = true;
1278
1279 /*
1280 * We can now mark all queues in the burst list as
1281 * belonging to a large burst.
1282 */
1283 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1284 burst_list_node)
1285 bfq_mark_bfqq_in_large_burst(bfqq_item);
1286 bfq_mark_bfqq_in_large_burst(bfqq);
1287
1288 /*
1289 * From now on, and until the current burst finishes, any
1290 * new queue being activated shortly after the last queue
1291 * was inserted in the burst can be immediately marked as
1292 * belonging to a large burst. So the burst list is not
1293 * needed any more. Remove it.
1294 */
1295 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1296 burst_list_node)
1297 hlist_del_init(&pos->burst_list_node);
1298 } else /*
1299 * Burst not yet large: add bfqq to the burst list. Do
1300 * not increment the ref counter for bfqq, because bfqq
1301 * is removed from the burst list before freeing bfqq
1302 * in put_queue.
1303 */
1304 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1305 }
1306
1307 /*
1308 * If many queues belonging to the same group happen to be created
1309 * shortly after each other, then the processes associated with these
1310 * queues have typically a common goal. In particular, bursts of queue
1311 * creations are usually caused by services or applications that spawn
1312 * many parallel threads/processes. Examples are systemd during boot,
1313 * or git grep. To help these processes get their job done as soon as
1314 * possible, it is usually better to not grant either weight-raising
1315 * or device idling to their queues, unless these queues must be
1316 * protected from the I/O flowing through other active queues.
1317 *
1318 * In this comment we describe, firstly, the reasons why this fact
1319 * holds, and, secondly, the next function, which implements the main
1320 * steps needed to properly mark these queues so that they can then be
1321 * treated in a different way.
1322 *
1323 * The above services or applications benefit mostly from a high
1324 * throughput: the quicker the requests of the activated queues are
1325 * cumulatively served, the sooner the target job of these queues gets
1326 * completed. As a consequence, weight-raising any of these queues,
1327 * which also implies idling the device for it, is almost always
1328 * counterproductive, unless there are other active queues to isolate
1329 * these new queues from. If there no other active queues, then
1330 * weight-raising these new queues just lowers throughput in most
1331 * cases.
1332 *
1333 * On the other hand, a burst of queue creations may be caused also by
1334 * the start of an application that does not consist of a lot of
1335 * parallel I/O-bound threads. In fact, with a complex application,
1336 * several short processes may need to be executed to start-up the
1337 * application. In this respect, to start an application as quickly as
1338 * possible, the best thing to do is in any case to privilege the I/O
1339 * related to the application with respect to all other
1340 * I/O. Therefore, the best strategy to start as quickly as possible
1341 * an application that causes a burst of queue creations is to
1342 * weight-raise all the queues created during the burst. This is the
1343 * exact opposite of the best strategy for the other type of bursts.
1344 *
1345 * In the end, to take the best action for each of the two cases, the
1346 * two types of bursts need to be distinguished. Fortunately, this
1347 * seems relatively easy, by looking at the sizes of the bursts. In
1348 * particular, we found a threshold such that only bursts with a
1349 * larger size than that threshold are apparently caused by
1350 * services or commands such as systemd or git grep. For brevity,
1351 * hereafter we call just 'large' these bursts. BFQ *does not*
1352 * weight-raise queues whose creation occurs in a large burst. In
1353 * addition, for each of these queues BFQ performs or does not perform
1354 * idling depending on which choice boosts the throughput more. The
1355 * exact choice depends on the device and request pattern at
1356 * hand.
1357 *
1358 * Unfortunately, false positives may occur while an interactive task
1359 * is starting (e.g., an application is being started). The
1360 * consequence is that the queues associated with the task do not
1361 * enjoy weight raising as expected. Fortunately these false positives
1362 * are very rare. They typically occur if some service happens to
1363 * start doing I/O exactly when the interactive task starts.
1364 *
1365 * Turning back to the next function, it is invoked only if there are
1366 * no active queues (apart from active queues that would belong to the
1367 * same, possible burst bfqq would belong to), and it implements all
1368 * the steps needed to detect the occurrence of a large burst and to
1369 * properly mark all the queues belonging to it (so that they can then
1370 * be treated in a different way). This goal is achieved by
1371 * maintaining a "burst list" that holds, temporarily, the queues that
1372 * belong to the burst in progress. The list is then used to mark
1373 * these queues as belonging to a large burst if the burst does become
1374 * large. The main steps are the following.
1375 *
1376 * . when the very first queue is created, the queue is inserted into the
1377 * list (as it could be the first queue in a possible burst)
1378 *
1379 * . if the current burst has not yet become large, and a queue Q that does
1380 * not yet belong to the burst is activated shortly after the last time
1381 * at which a new queue entered the burst list, then the function appends
1382 * Q to the burst list
1383 *
1384 * . if, as a consequence of the previous step, the burst size reaches
1385 * the large-burst threshold, then
1386 *
1387 * . all the queues in the burst list are marked as belonging to a
1388 * large burst
1389 *
1390 * . the burst list is deleted; in fact, the burst list already served
1391 * its purpose (keeping temporarily track of the queues in a burst,
1392 * so as to be able to mark them as belonging to a large burst in the
1393 * previous sub-step), and now is not needed any more
1394 *
1395 * . the device enters a large-burst mode
1396 *
1397 * . if a queue Q that does not belong to the burst is created while
1398 * the device is in large-burst mode and shortly after the last time
1399 * at which a queue either entered the burst list or was marked as
1400 * belonging to the current large burst, then Q is immediately marked
1401 * as belonging to a large burst.
1402 *
1403 * . if a queue Q that does not belong to the burst is created a while
1404 * later, i.e., not shortly after, than the last time at which a queue
1405 * either entered the burst list or was marked as belonging to the
1406 * current large burst, then the current burst is deemed as finished and:
1407 *
1408 * . the large-burst mode is reset if set
1409 *
1410 * . the burst list is emptied
1411 *
1412 * . Q is inserted in the burst list, as Q may be the first queue
1413 * in a possible new burst (then the burst list contains just Q
1414 * after this step).
1415 */
bfq_handle_burst(struct bfq_data * bfqd,struct bfq_queue * bfqq)1416 static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1417 {
1418 /*
1419 * If bfqq is already in the burst list or is part of a large
1420 * burst, or finally has just been split, then there is
1421 * nothing else to do.
1422 */
1423 if (!hlist_unhashed(&bfqq->burst_list_node) ||
1424 bfq_bfqq_in_large_burst(bfqq) ||
1425 time_is_after_eq_jiffies(bfqq->split_time +
1426 msecs_to_jiffies(10)))
1427 return;
1428
1429 /*
1430 * If bfqq's creation happens late enough, or bfqq belongs to
1431 * a different group than the burst group, then the current
1432 * burst is finished, and related data structures must be
1433 * reset.
1434 *
1435 * In this respect, consider the special case where bfqq is
1436 * the very first queue created after BFQ is selected for this
1437 * device. In this case, last_ins_in_burst and
1438 * burst_parent_entity are not yet significant when we get
1439 * here. But it is easy to verify that, whether or not the
1440 * following condition is true, bfqq will end up being
1441 * inserted into the burst list. In particular the list will
1442 * happen to contain only bfqq. And this is exactly what has
1443 * to happen, as bfqq may be the first queue of the first
1444 * burst.
1445 */
1446 if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1447 bfqd->bfq_burst_interval) ||
1448 bfqq->entity.parent != bfqd->burst_parent_entity) {
1449 bfqd->large_burst = false;
1450 bfq_reset_burst_list(bfqd, bfqq);
1451 goto end;
1452 }
1453
1454 /*
1455 * If we get here, then bfqq is being activated shortly after the
1456 * last queue. So, if the current burst is also large, we can mark
1457 * bfqq as belonging to this large burst immediately.
1458 */
1459 if (bfqd->large_burst) {
1460 bfq_mark_bfqq_in_large_burst(bfqq);
1461 goto end;
1462 }
1463
1464 /*
1465 * If we get here, then a large-burst state has not yet been
1466 * reached, but bfqq is being activated shortly after the last
1467 * queue. Then we add bfqq to the burst.
1468 */
1469 bfq_add_to_burst(bfqd, bfqq);
1470 end:
1471 /*
1472 * At this point, bfqq either has been added to the current
1473 * burst or has caused the current burst to terminate and a
1474 * possible new burst to start. In particular, in the second
1475 * case, bfqq has become the first queue in the possible new
1476 * burst. In both cases last_ins_in_burst needs to be moved
1477 * forward.
1478 */
1479 bfqd->last_ins_in_burst = jiffies;
1480 }
1481
bfq_bfqq_budget_left(struct bfq_queue * bfqq)1482 static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1483 {
1484 struct bfq_entity *entity = &bfqq->entity;
1485
1486 return entity->budget - entity->service;
1487 }
1488
1489 /*
1490 * If enough samples have been computed, return the current max budget
1491 * stored in bfqd, which is dynamically updated according to the
1492 * estimated disk peak rate; otherwise return the default max budget
1493 */
bfq_max_budget(struct bfq_data * bfqd)1494 static int bfq_max_budget(struct bfq_data *bfqd)
1495 {
1496 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1497 return bfq_default_max_budget;
1498 else
1499 return bfqd->bfq_max_budget;
1500 }
1501
1502 /*
1503 * Return min budget, which is a fraction of the current or default
1504 * max budget (trying with 1/32)
1505 */
bfq_min_budget(struct bfq_data * bfqd)1506 static int bfq_min_budget(struct bfq_data *bfqd)
1507 {
1508 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1509 return bfq_default_max_budget / 32;
1510 else
1511 return bfqd->bfq_max_budget / 32;
1512 }
1513
1514 /*
1515 * The next function, invoked after the input queue bfqq switches from
1516 * idle to busy, updates the budget of bfqq. The function also tells
1517 * whether the in-service queue should be expired, by returning
1518 * true. The purpose of expiring the in-service queue is to give bfqq
1519 * the chance to possibly preempt the in-service queue, and the reason
1520 * for preempting the in-service queue is to achieve one of the two
1521 * goals below.
1522 *
1523 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1524 * expired because it has remained idle. In particular, bfqq may have
1525 * expired for one of the following two reasons:
1526 *
1527 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1528 * and did not make it to issue a new request before its last
1529 * request was served;
1530 *
1531 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1532 * a new request before the expiration of the idling-time.
1533 *
1534 * Even if bfqq has expired for one of the above reasons, the process
1535 * associated with the queue may be however issuing requests greedily,
1536 * and thus be sensitive to the bandwidth it receives (bfqq may have
1537 * remained idle for other reasons: CPU high load, bfqq not enjoying
1538 * idling, I/O throttling somewhere in the path from the process to
1539 * the I/O scheduler, ...). But if, after every expiration for one of
1540 * the above two reasons, bfqq has to wait for the service of at least
1541 * one full budget of another queue before being served again, then
1542 * bfqq is likely to get a much lower bandwidth or resource time than
1543 * its reserved ones. To address this issue, two countermeasures need
1544 * to be taken.
1545 *
1546 * First, the budget and the timestamps of bfqq need to be updated in
1547 * a special way on bfqq reactivation: they need to be updated as if
1548 * bfqq did not remain idle and did not expire. In fact, if they are
1549 * computed as if bfqq expired and remained idle until reactivation,
1550 * then the process associated with bfqq is treated as if, instead of
1551 * being greedy, it stopped issuing requests when bfqq remained idle,
1552 * and restarts issuing requests only on this reactivation. In other
1553 * words, the scheduler does not help the process recover the "service
1554 * hole" between bfqq expiration and reactivation. As a consequence,
1555 * the process receives a lower bandwidth than its reserved one. In
1556 * contrast, to recover this hole, the budget must be updated as if
1557 * bfqq was not expired at all before this reactivation, i.e., it must
1558 * be set to the value of the remaining budget when bfqq was
1559 * expired. Along the same line, timestamps need to be assigned the
1560 * value they had the last time bfqq was selected for service, i.e.,
1561 * before last expiration. Thus timestamps need to be back-shifted
1562 * with respect to their normal computation (see [1] for more details
1563 * on this tricky aspect).
1564 *
1565 * Secondly, to allow the process to recover the hole, the in-service
1566 * queue must be expired too, to give bfqq the chance to preempt it
1567 * immediately. In fact, if bfqq has to wait for a full budget of the
1568 * in-service queue to be completed, then it may become impossible to
1569 * let the process recover the hole, even if the back-shifted
1570 * timestamps of bfqq are lower than those of the in-service queue. If
1571 * this happens for most or all of the holes, then the process may not
1572 * receive its reserved bandwidth. In this respect, it is worth noting
1573 * that, being the service of outstanding requests unpreemptible, a
1574 * little fraction of the holes may however be unrecoverable, thereby
1575 * causing a little loss of bandwidth.
1576 *
1577 * The last important point is detecting whether bfqq does need this
1578 * bandwidth recovery. In this respect, the next function deems the
1579 * process associated with bfqq greedy, and thus allows it to recover
1580 * the hole, if: 1) the process is waiting for the arrival of a new
1581 * request (which implies that bfqq expired for one of the above two
1582 * reasons), and 2) such a request has arrived soon. The first
1583 * condition is controlled through the flag non_blocking_wait_rq,
1584 * while the second through the flag arrived_in_time. If both
1585 * conditions hold, then the function computes the budget in the
1586 * above-described special way, and signals that the in-service queue
1587 * should be expired. Timestamp back-shifting is done later in
1588 * __bfq_activate_entity.
1589 *
1590 * 2. Reduce latency. Even if timestamps are not backshifted to let
1591 * the process associated with bfqq recover a service hole, bfqq may
1592 * however happen to have, after being (re)activated, a lower finish
1593 * timestamp than the in-service queue. That is, the next budget of
1594 * bfqq may have to be completed before the one of the in-service
1595 * queue. If this is the case, then preempting the in-service queue
1596 * allows this goal to be achieved, apart from the unpreemptible,
1597 * outstanding requests mentioned above.
1598 *
1599 * Unfortunately, regardless of which of the above two goals one wants
1600 * to achieve, service trees need first to be updated to know whether
1601 * the in-service queue must be preempted. To have service trees
1602 * correctly updated, the in-service queue must be expired and
1603 * rescheduled, and bfqq must be scheduled too. This is one of the
1604 * most costly operations (in future versions, the scheduling
1605 * mechanism may be re-designed in such a way to make it possible to
1606 * know whether preemption is needed without needing to update service
1607 * trees). In addition, queue preemptions almost always cause random
1608 * I/O, which may in turn cause loss of throughput. Finally, there may
1609 * even be no in-service queue when the next function is invoked (so,
1610 * no queue to compare timestamps with). Because of these facts, the
1611 * next function adopts the following simple scheme to avoid costly
1612 * operations, too frequent preemptions and too many dependencies on
1613 * the state of the scheduler: it requests the expiration of the
1614 * in-service queue (unconditionally) only for queues that need to
1615 * recover a hole. Then it delegates to other parts of the code the
1616 * responsibility of handling the above case 2.
1617 */
bfq_bfqq_update_budg_for_activation(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool arrived_in_time)1618 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1619 struct bfq_queue *bfqq,
1620 bool arrived_in_time)
1621 {
1622 struct bfq_entity *entity = &bfqq->entity;
1623
1624 /*
1625 * In the next compound condition, we check also whether there
1626 * is some budget left, because otherwise there is no point in
1627 * trying to go on serving bfqq with this same budget: bfqq
1628 * would be expired immediately after being selected for
1629 * service. This would only cause useless overhead.
1630 */
1631 if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1632 bfq_bfqq_budget_left(bfqq) > 0) {
1633 /*
1634 * We do not clear the flag non_blocking_wait_rq here, as
1635 * the latter is used in bfq_activate_bfqq to signal
1636 * that timestamps need to be back-shifted (and is
1637 * cleared right after).
1638 */
1639
1640 /*
1641 * In next assignment we rely on that either
1642 * entity->service or entity->budget are not updated
1643 * on expiration if bfqq is empty (see
1644 * __bfq_bfqq_recalc_budget). Thus both quantities
1645 * remain unchanged after such an expiration, and the
1646 * following statement therefore assigns to
1647 * entity->budget the remaining budget on such an
1648 * expiration.
1649 */
1650 entity->budget = min_t(unsigned long,
1651 bfq_bfqq_budget_left(bfqq),
1652 bfqq->max_budget);
1653
1654 /*
1655 * At this point, we have used entity->service to get
1656 * the budget left (needed for updating
1657 * entity->budget). Thus we finally can, and have to,
1658 * reset entity->service. The latter must be reset
1659 * because bfqq would otherwise be charged again for
1660 * the service it has received during its previous
1661 * service slot(s).
1662 */
1663 entity->service = 0;
1664
1665 return true;
1666 }
1667
1668 /*
1669 * We can finally complete expiration, by setting service to 0.
1670 */
1671 entity->service = 0;
1672 entity->budget = max_t(unsigned long, bfqq->max_budget,
1673 bfq_serv_to_charge(bfqq->next_rq, bfqq));
1674 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1675 return false;
1676 }
1677
1678 /*
1679 * Return the farthest past time instant according to jiffies
1680 * macros.
1681 */
bfq_smallest_from_now(void)1682 static unsigned long bfq_smallest_from_now(void)
1683 {
1684 return jiffies - MAX_JIFFY_OFFSET;
1685 }
1686
bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data * bfqd,struct bfq_queue * bfqq,unsigned int old_wr_coeff,bool wr_or_deserves_wr,bool interactive,bool in_burst,bool soft_rt)1687 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1688 struct bfq_queue *bfqq,
1689 unsigned int old_wr_coeff,
1690 bool wr_or_deserves_wr,
1691 bool interactive,
1692 bool in_burst,
1693 bool soft_rt)
1694 {
1695 if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1696 /* start a weight-raising period */
1697 if (interactive) {
1698 bfqq->service_from_wr = 0;
1699 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1700 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1701 } else {
1702 /*
1703 * No interactive weight raising in progress
1704 * here: assign minus infinity to
1705 * wr_start_at_switch_to_srt, to make sure
1706 * that, at the end of the soft-real-time
1707 * weight raising periods that is starting
1708 * now, no interactive weight-raising period
1709 * may be wrongly considered as still in
1710 * progress (and thus actually started by
1711 * mistake).
1712 */
1713 bfqq->wr_start_at_switch_to_srt =
1714 bfq_smallest_from_now();
1715 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1716 BFQ_SOFTRT_WEIGHT_FACTOR;
1717 bfqq->wr_cur_max_time =
1718 bfqd->bfq_wr_rt_max_time;
1719 }
1720
1721 /*
1722 * If needed, further reduce budget to make sure it is
1723 * close to bfqq's backlog, so as to reduce the
1724 * scheduling-error component due to a too large
1725 * budget. Do not care about throughput consequences,
1726 * but only about latency. Finally, do not assign a
1727 * too small budget either, to avoid increasing
1728 * latency by causing too frequent expirations.
1729 */
1730 bfqq->entity.budget = min_t(unsigned long,
1731 bfqq->entity.budget,
1732 2 * bfq_min_budget(bfqd));
1733 } else if (old_wr_coeff > 1) {
1734 if (interactive) { /* update wr coeff and duration */
1735 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1736 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1737 } else if (in_burst)
1738 bfqq->wr_coeff = 1;
1739 else if (soft_rt) {
1740 /*
1741 * The application is now or still meeting the
1742 * requirements for being deemed soft rt. We
1743 * can then correctly and safely (re)charge
1744 * the weight-raising duration for the
1745 * application with the weight-raising
1746 * duration for soft rt applications.
1747 *
1748 * In particular, doing this recharge now, i.e.,
1749 * before the weight-raising period for the
1750 * application finishes, reduces the probability
1751 * of the following negative scenario:
1752 * 1) the weight of a soft rt application is
1753 * raised at startup (as for any newly
1754 * created application),
1755 * 2) since the application is not interactive,
1756 * at a certain time weight-raising is
1757 * stopped for the application,
1758 * 3) at that time the application happens to
1759 * still have pending requests, and hence
1760 * is destined to not have a chance to be
1761 * deemed soft rt before these requests are
1762 * completed (see the comments to the
1763 * function bfq_bfqq_softrt_next_start()
1764 * for details on soft rt detection),
1765 * 4) these pending requests experience a high
1766 * latency because the application is not
1767 * weight-raised while they are pending.
1768 */
1769 if (bfqq->wr_cur_max_time !=
1770 bfqd->bfq_wr_rt_max_time) {
1771 bfqq->wr_start_at_switch_to_srt =
1772 bfqq->last_wr_start_finish;
1773
1774 bfqq->wr_cur_max_time =
1775 bfqd->bfq_wr_rt_max_time;
1776 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1777 BFQ_SOFTRT_WEIGHT_FACTOR;
1778 }
1779 bfqq->last_wr_start_finish = jiffies;
1780 }
1781 }
1782 }
1783
bfq_bfqq_idle_for_long_time(struct bfq_data * bfqd,struct bfq_queue * bfqq)1784 static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1785 struct bfq_queue *bfqq)
1786 {
1787 return bfqq->dispatched == 0 &&
1788 time_is_before_jiffies(
1789 bfqq->budget_timeout +
1790 bfqd->bfq_wr_min_idle_time);
1791 }
1792
1793
1794 /*
1795 * Return true if bfqq is in a higher priority class, or has a higher
1796 * weight than the in-service queue.
1797 */
bfq_bfqq_higher_class_or_weight(struct bfq_queue * bfqq,struct bfq_queue * in_serv_bfqq)1798 static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1799 struct bfq_queue *in_serv_bfqq)
1800 {
1801 int bfqq_weight, in_serv_weight;
1802
1803 if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1804 return true;
1805
1806 if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1807 bfqq_weight = bfqq->entity.weight;
1808 in_serv_weight = in_serv_bfqq->entity.weight;
1809 } else {
1810 if (bfqq->entity.parent)
1811 bfqq_weight = bfqq->entity.parent->weight;
1812 else
1813 bfqq_weight = bfqq->entity.weight;
1814 if (in_serv_bfqq->entity.parent)
1815 in_serv_weight = in_serv_bfqq->entity.parent->weight;
1816 else
1817 in_serv_weight = in_serv_bfqq->entity.weight;
1818 }
1819
1820 return bfqq_weight > in_serv_weight;
1821 }
1822
1823 static bool bfq_better_to_idle(struct bfq_queue *bfqq);
1824
bfq_bfqq_handle_idle_busy_switch(struct bfq_data * bfqd,struct bfq_queue * bfqq,int old_wr_coeff,struct request * rq,bool * interactive)1825 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1826 struct bfq_queue *bfqq,
1827 int old_wr_coeff,
1828 struct request *rq,
1829 bool *interactive)
1830 {
1831 bool soft_rt, in_burst, wr_or_deserves_wr,
1832 bfqq_wants_to_preempt,
1833 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1834 /*
1835 * See the comments on
1836 * bfq_bfqq_update_budg_for_activation for
1837 * details on the usage of the next variable.
1838 */
1839 arrived_in_time = ktime_get_ns() <=
1840 bfqq->ttime.last_end_request +
1841 bfqd->bfq_slice_idle * 3;
1842
1843
1844 /*
1845 * bfqq deserves to be weight-raised if:
1846 * - it is sync,
1847 * - it does not belong to a large burst,
1848 * - it has been idle for enough time or is soft real-time,
1849 * - is linked to a bfq_io_cq (it is not shared in any sense),
1850 * - has a default weight (otherwise we assume the user wanted
1851 * to control its weight explicitly)
1852 */
1853 in_burst = bfq_bfqq_in_large_burst(bfqq);
1854 soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1855 !BFQQ_TOTALLY_SEEKY(bfqq) &&
1856 !in_burst &&
1857 time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1858 bfqq->dispatched == 0 &&
1859 bfqq->entity.new_weight == 40;
1860 *interactive = !in_burst && idle_for_long_time &&
1861 bfqq->entity.new_weight == 40;
1862 /*
1863 * Merged bfq_queues are kept out of weight-raising
1864 * (low-latency) mechanisms. The reason is that these queues
1865 * are usually created for non-interactive and
1866 * non-soft-real-time tasks. Yet this is not the case for
1867 * stably-merged queues. These queues are merged just because
1868 * they are created shortly after each other. So they may
1869 * easily serve the I/O of an interactive or soft-real time
1870 * application, if the application happens to spawn multiple
1871 * processes. So let also stably-merged queued enjoy weight
1872 * raising.
1873 */
1874 wr_or_deserves_wr = bfqd->low_latency &&
1875 (bfqq->wr_coeff > 1 ||
1876 (bfq_bfqq_sync(bfqq) &&
1877 (bfqq->bic || RQ_BIC(rq)->stably_merged) &&
1878 (*interactive || soft_rt)));
1879
1880 /*
1881 * Using the last flag, update budget and check whether bfqq
1882 * may want to preempt the in-service queue.
1883 */
1884 bfqq_wants_to_preempt =
1885 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1886 arrived_in_time);
1887
1888 /*
1889 * If bfqq happened to be activated in a burst, but has been
1890 * idle for much more than an interactive queue, then we
1891 * assume that, in the overall I/O initiated in the burst, the
1892 * I/O associated with bfqq is finished. So bfqq does not need
1893 * to be treated as a queue belonging to a burst
1894 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1895 * if set, and remove bfqq from the burst list if it's
1896 * there. We do not decrement burst_size, because the fact
1897 * that bfqq does not need to belong to the burst list any
1898 * more does not invalidate the fact that bfqq was created in
1899 * a burst.
1900 */
1901 if (likely(!bfq_bfqq_just_created(bfqq)) &&
1902 idle_for_long_time &&
1903 time_is_before_jiffies(
1904 bfqq->budget_timeout +
1905 msecs_to_jiffies(10000))) {
1906 hlist_del_init(&bfqq->burst_list_node);
1907 bfq_clear_bfqq_in_large_burst(bfqq);
1908 }
1909
1910 bfq_clear_bfqq_just_created(bfqq);
1911
1912 if (bfqd->low_latency) {
1913 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1914 /* wraparound */
1915 bfqq->split_time =
1916 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1917
1918 if (time_is_before_jiffies(bfqq->split_time +
1919 bfqd->bfq_wr_min_idle_time)) {
1920 bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1921 old_wr_coeff,
1922 wr_or_deserves_wr,
1923 *interactive,
1924 in_burst,
1925 soft_rt);
1926
1927 if (old_wr_coeff != bfqq->wr_coeff)
1928 bfqq->entity.prio_changed = 1;
1929 }
1930 }
1931
1932 bfqq->last_idle_bklogged = jiffies;
1933 bfqq->service_from_backlogged = 0;
1934 bfq_clear_bfqq_softrt_update(bfqq);
1935
1936 bfq_add_bfqq_busy(bfqq);
1937
1938 /*
1939 * Expire in-service queue if preemption may be needed for
1940 * guarantees or throughput. As for guarantees, we care
1941 * explicitly about two cases. The first is that bfqq has to
1942 * recover a service hole, as explained in the comments on
1943 * bfq_bfqq_update_budg_for_activation(), i.e., that
1944 * bfqq_wants_to_preempt is true. However, if bfqq does not
1945 * carry time-critical I/O, then bfqq's bandwidth is less
1946 * important than that of queues that carry time-critical I/O.
1947 * So, as a further constraint, we consider this case only if
1948 * bfqq is at least as weight-raised, i.e., at least as time
1949 * critical, as the in-service queue.
1950 *
1951 * The second case is that bfqq is in a higher priority class,
1952 * or has a higher weight than the in-service queue. If this
1953 * condition does not hold, we don't care because, even if
1954 * bfqq does not start to be served immediately, the resulting
1955 * delay for bfqq's I/O is however lower or much lower than
1956 * the ideal completion time to be guaranteed to bfqq's I/O.
1957 *
1958 * In both cases, preemption is needed only if, according to
1959 * the timestamps of both bfqq and of the in-service queue,
1960 * bfqq actually is the next queue to serve. So, to reduce
1961 * useless preemptions, the return value of
1962 * next_queue_may_preempt() is considered in the next compound
1963 * condition too. Yet next_queue_may_preempt() just checks a
1964 * simple, necessary condition for bfqq to be the next queue
1965 * to serve. In fact, to evaluate a sufficient condition, the
1966 * timestamps of the in-service queue would need to be
1967 * updated, and this operation is quite costly (see the
1968 * comments on bfq_bfqq_update_budg_for_activation()).
1969 *
1970 * As for throughput, we ask bfq_better_to_idle() whether we
1971 * still need to plug I/O dispatching. If bfq_better_to_idle()
1972 * says no, then plugging is not needed any longer, either to
1973 * boost throughput or to perserve service guarantees. Then
1974 * the best option is to stop plugging I/O, as not doing so
1975 * would certainly lower throughput. We may end up in this
1976 * case if: (1) upon a dispatch attempt, we detected that it
1977 * was better to plug I/O dispatch, and to wait for a new
1978 * request to arrive for the currently in-service queue, but
1979 * (2) this switch of bfqq to busy changes the scenario.
1980 */
1981 if (bfqd->in_service_queue &&
1982 ((bfqq_wants_to_preempt &&
1983 bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1984 bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue) ||
1985 !bfq_better_to_idle(bfqd->in_service_queue)) &&
1986 next_queue_may_preempt(bfqd))
1987 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1988 false, BFQQE_PREEMPTED);
1989 }
1990
bfq_reset_inject_limit(struct bfq_data * bfqd,struct bfq_queue * bfqq)1991 static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1992 struct bfq_queue *bfqq)
1993 {
1994 /* invalidate baseline total service time */
1995 bfqq->last_serv_time_ns = 0;
1996
1997 /*
1998 * Reset pointer in case we are waiting for
1999 * some request completion.
2000 */
2001 bfqd->waited_rq = NULL;
2002
2003 /*
2004 * If bfqq has a short think time, then start by setting the
2005 * inject limit to 0 prudentially, because the service time of
2006 * an injected I/O request may be higher than the think time
2007 * of bfqq, and therefore, if one request was injected when
2008 * bfqq remains empty, this injected request might delay the
2009 * service of the next I/O request for bfqq significantly. In
2010 * case bfqq can actually tolerate some injection, then the
2011 * adaptive update will however raise the limit soon. This
2012 * lucky circumstance holds exactly because bfqq has a short
2013 * think time, and thus, after remaining empty, is likely to
2014 * get new I/O enqueued---and then completed---before being
2015 * expired. This is the very pattern that gives the
2016 * limit-update algorithm the chance to measure the effect of
2017 * injection on request service times, and then to update the
2018 * limit accordingly.
2019 *
2020 * However, in the following special case, the inject limit is
2021 * left to 1 even if the think time is short: bfqq's I/O is
2022 * synchronized with that of some other queue, i.e., bfqq may
2023 * receive new I/O only after the I/O of the other queue is
2024 * completed. Keeping the inject limit to 1 allows the
2025 * blocking I/O to be served while bfqq is in service. And
2026 * this is very convenient both for bfqq and for overall
2027 * throughput, as explained in detail in the comments in
2028 * bfq_update_has_short_ttime().
2029 *
2030 * On the opposite end, if bfqq has a long think time, then
2031 * start directly by 1, because:
2032 * a) on the bright side, keeping at most one request in
2033 * service in the drive is unlikely to cause any harm to the
2034 * latency of bfqq's requests, as the service time of a single
2035 * request is likely to be lower than the think time of bfqq;
2036 * b) on the downside, after becoming empty, bfqq is likely to
2037 * expire before getting its next request. With this request
2038 * arrival pattern, it is very hard to sample total service
2039 * times and update the inject limit accordingly (see comments
2040 * on bfq_update_inject_limit()). So the limit is likely to be
2041 * never, or at least seldom, updated. As a consequence, by
2042 * setting the limit to 1, we avoid that no injection ever
2043 * occurs with bfqq. On the downside, this proactive step
2044 * further reduces chances to actually compute the baseline
2045 * total service time. Thus it reduces chances to execute the
2046 * limit-update algorithm and possibly raise the limit to more
2047 * than 1.
2048 */
2049 if (bfq_bfqq_has_short_ttime(bfqq))
2050 bfqq->inject_limit = 0;
2051 else
2052 bfqq->inject_limit = 1;
2053
2054 bfqq->decrease_time_jif = jiffies;
2055 }
2056
bfq_update_io_intensity(struct bfq_queue * bfqq,u64 now_ns)2057 static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
2058 {
2059 u64 tot_io_time = now_ns - bfqq->io_start_time;
2060
2061 if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
2062 bfqq->tot_idle_time +=
2063 now_ns - bfqq->ttime.last_end_request;
2064
2065 if (unlikely(bfq_bfqq_just_created(bfqq)))
2066 return;
2067
2068 /*
2069 * Must be busy for at least about 80% of the time to be
2070 * considered I/O bound.
2071 */
2072 if (bfqq->tot_idle_time * 5 > tot_io_time)
2073 bfq_clear_bfqq_IO_bound(bfqq);
2074 else
2075 bfq_mark_bfqq_IO_bound(bfqq);
2076
2077 /*
2078 * Keep an observation window of at most 200 ms in the past
2079 * from now.
2080 */
2081 if (tot_io_time > 200 * NSEC_PER_MSEC) {
2082 bfqq->io_start_time = now_ns - (tot_io_time>>1);
2083 bfqq->tot_idle_time >>= 1;
2084 }
2085 }
2086
2087 /*
2088 * Detect whether bfqq's I/O seems synchronized with that of some
2089 * other queue, i.e., whether bfqq, after remaining empty, happens to
2090 * receive new I/O only right after some I/O request of the other
2091 * queue has been completed. We call waker queue the other queue, and
2092 * we assume, for simplicity, that bfqq may have at most one waker
2093 * queue.
2094 *
2095 * A remarkable throughput boost can be reached by unconditionally
2096 * injecting the I/O of the waker queue, every time a new
2097 * bfq_dispatch_request happens to be invoked while I/O is being
2098 * plugged for bfqq. In addition to boosting throughput, this
2099 * unblocks bfqq's I/O, thereby improving bandwidth and latency for
2100 * bfqq. Note that these same results may be achieved with the general
2101 * injection mechanism, but less effectively. For details on this
2102 * aspect, see the comments on the choice of the queue for injection
2103 * in bfq_select_queue().
2104 *
2105 * Turning back to the detection of a waker queue, a queue Q is deemed as a
2106 * waker queue for bfqq if, for three consecutive times, bfqq happens to become
2107 * non empty right after a request of Q has been completed within given
2108 * timeout. In this respect, even if bfqq is empty, we do not check for a waker
2109 * if it still has some in-flight I/O. In fact, in this case bfqq is actually
2110 * still being served by the drive, and may receive new I/O on the completion
2111 * of some of the in-flight requests. In particular, on the first time, Q is
2112 * tentatively set as a candidate waker queue, while on the third consecutive
2113 * time that Q is detected, the field waker_bfqq is set to Q, to confirm that Q
2114 * is a waker queue for bfqq. These detection steps are performed only if bfqq
2115 * has a long think time, so as to make it more likely that bfqq's I/O is
2116 * actually being blocked by a synchronization. This last filter, plus the
2117 * above three-times requirement and time limit for detection, make false
2118 * positives less likely.
2119 *
2120 * NOTE
2121 *
2122 * The sooner a waker queue is detected, the sooner throughput can be
2123 * boosted by injecting I/O from the waker queue. Fortunately,
2124 * detection is likely to be actually fast, for the following
2125 * reasons. While blocked by synchronization, bfqq has a long think
2126 * time. This implies that bfqq's inject limit is at least equal to 1
2127 * (see the comments in bfq_update_inject_limit()). So, thanks to
2128 * injection, the waker queue is likely to be served during the very
2129 * first I/O-plugging time interval for bfqq. This triggers the first
2130 * step of the detection mechanism. Thanks again to injection, the
2131 * candidate waker queue is then likely to be confirmed no later than
2132 * during the next I/O-plugging interval for bfqq.
2133 *
2134 * ISSUE
2135 *
2136 * On queue merging all waker information is lost.
2137 */
bfq_check_waker(struct bfq_data * bfqd,struct bfq_queue * bfqq,u64 now_ns)2138 static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2139 u64 now_ns)
2140 {
2141 char waker_name[MAX_BFQQ_NAME_LENGTH];
2142
2143 if (!bfqd->last_completed_rq_bfqq ||
2144 bfqd->last_completed_rq_bfqq == bfqq ||
2145 bfq_bfqq_has_short_ttime(bfqq) ||
2146 now_ns - bfqd->last_completion >= 4 * NSEC_PER_MSEC)
2147 return;
2148
2149 /*
2150 * We reset waker detection logic also if too much time has passed
2151 * since the first detection. If wakeups are rare, pointless idling
2152 * doesn't hurt throughput that much. The condition below makes sure
2153 * we do not uselessly idle blocking waker in more than 1/64 cases.
2154 */
2155 if (bfqd->last_completed_rq_bfqq !=
2156 bfqq->tentative_waker_bfqq ||
2157 now_ns > bfqq->waker_detection_started +
2158 128 * (u64)bfqd->bfq_slice_idle) {
2159 /*
2160 * First synchronization detected with a
2161 * candidate waker queue, or with a different
2162 * candidate waker queue from the current one.
2163 */
2164 bfqq->tentative_waker_bfqq =
2165 bfqd->last_completed_rq_bfqq;
2166 bfqq->num_waker_detections = 1;
2167 bfqq->waker_detection_started = now_ns;
2168 bfq_bfqq_name(bfqq->tentative_waker_bfqq, waker_name,
2169 MAX_BFQQ_NAME_LENGTH);
2170 bfq_log_bfqq(bfqd, bfqq, "set tentative waker %s", waker_name);
2171 } else /* Same tentative waker queue detected again */
2172 bfqq->num_waker_detections++;
2173
2174 if (bfqq->num_waker_detections == 3) {
2175 bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
2176 bfqq->tentative_waker_bfqq = NULL;
2177 bfq_bfqq_name(bfqq->waker_bfqq, waker_name,
2178 MAX_BFQQ_NAME_LENGTH);
2179 bfq_log_bfqq(bfqd, bfqq, "set waker %s", waker_name);
2180
2181 /*
2182 * If the waker queue disappears, then
2183 * bfqq->waker_bfqq must be reset. To
2184 * this goal, we maintain in each
2185 * waker queue a list, woken_list, of
2186 * all the queues that reference the
2187 * waker queue through their
2188 * waker_bfqq pointer. When the waker
2189 * queue exits, the waker_bfqq pointer
2190 * of all the queues in the woken_list
2191 * is reset.
2192 *
2193 * In addition, if bfqq is already in
2194 * the woken_list of a waker queue,
2195 * then, before being inserted into
2196 * the woken_list of a new waker
2197 * queue, bfqq must be removed from
2198 * the woken_list of the old waker
2199 * queue.
2200 */
2201 if (!hlist_unhashed(&bfqq->woken_list_node))
2202 hlist_del_init(&bfqq->woken_list_node);
2203 hlist_add_head(&bfqq->woken_list_node,
2204 &bfqd->last_completed_rq_bfqq->woken_list);
2205 }
2206 }
2207
bfq_add_request(struct request * rq)2208 static void bfq_add_request(struct request *rq)
2209 {
2210 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2211 struct bfq_data *bfqd = bfqq->bfqd;
2212 struct request *next_rq, *prev;
2213 unsigned int old_wr_coeff = bfqq->wr_coeff;
2214 bool interactive = false;
2215 u64 now_ns = ktime_get_ns();
2216
2217 bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
2218 bfqq->queued[rq_is_sync(rq)]++;
2219 /*
2220 * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2221 * may be read without holding the lock in bfq_has_work().
2222 */
2223 WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
2224
2225 if (bfq_bfqq_sync(bfqq) && RQ_BIC(rq)->requests <= 1) {
2226 bfq_check_waker(bfqd, bfqq, now_ns);
2227
2228 /*
2229 * Periodically reset inject limit, to make sure that
2230 * the latter eventually drops in case workload
2231 * changes, see step (3) in the comments on
2232 * bfq_update_inject_limit().
2233 */
2234 if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2235 msecs_to_jiffies(1000)))
2236 bfq_reset_inject_limit(bfqd, bfqq);
2237
2238 /*
2239 * The following conditions must hold to setup a new
2240 * sampling of total service time, and then a new
2241 * update of the inject limit:
2242 * - bfqq is in service, because the total service
2243 * time is evaluated only for the I/O requests of
2244 * the queues in service;
2245 * - this is the right occasion to compute or to
2246 * lower the baseline total service time, because
2247 * there are actually no requests in the drive,
2248 * or
2249 * the baseline total service time is available, and
2250 * this is the right occasion to compute the other
2251 * quantity needed to update the inject limit, i.e.,
2252 * the total service time caused by the amount of
2253 * injection allowed by the current value of the
2254 * limit. It is the right occasion because injection
2255 * has actually been performed during the service
2256 * hole, and there are still in-flight requests,
2257 * which are very likely to be exactly the injected
2258 * requests, or part of them;
2259 * - the minimum interval for sampling the total
2260 * service time and updating the inject limit has
2261 * elapsed.
2262 */
2263 if (bfqq == bfqd->in_service_queue &&
2264 (bfqd->rq_in_driver == 0 ||
2265 (bfqq->last_serv_time_ns > 0 &&
2266 bfqd->rqs_injected && bfqd->rq_in_driver > 0)) &&
2267 time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2268 msecs_to_jiffies(10))) {
2269 bfqd->last_empty_occupied_ns = ktime_get_ns();
2270 /*
2271 * Start the state machine for measuring the
2272 * total service time of rq: setting
2273 * wait_dispatch will cause bfqd->waited_rq to
2274 * be set when rq will be dispatched.
2275 */
2276 bfqd->wait_dispatch = true;
2277 /*
2278 * If there is no I/O in service in the drive,
2279 * then possible injection occurred before the
2280 * arrival of rq will not affect the total
2281 * service time of rq. So the injection limit
2282 * must not be updated as a function of such
2283 * total service time, unless new injection
2284 * occurs before rq is completed. To have the
2285 * injection limit updated only in the latter
2286 * case, reset rqs_injected here (rqs_injected
2287 * will be set in case injection is performed
2288 * on bfqq before rq is completed).
2289 */
2290 if (bfqd->rq_in_driver == 0)
2291 bfqd->rqs_injected = false;
2292 }
2293 }
2294
2295 if (bfq_bfqq_sync(bfqq))
2296 bfq_update_io_intensity(bfqq, now_ns);
2297
2298 elv_rb_add(&bfqq->sort_list, rq);
2299
2300 /*
2301 * Check if this request is a better next-serve candidate.
2302 */
2303 prev = bfqq->next_rq;
2304 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
2305 bfqq->next_rq = next_rq;
2306
2307 /*
2308 * Adjust priority tree position, if next_rq changes.
2309 * See comments on bfq_pos_tree_add_move() for the unlikely().
2310 */
2311 if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2312 bfq_pos_tree_add_move(bfqd, bfqq);
2313
2314 if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2315 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2316 rq, &interactive);
2317 else {
2318 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2319 time_is_before_jiffies(
2320 bfqq->last_wr_start_finish +
2321 bfqd->bfq_wr_min_inter_arr_async)) {
2322 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2323 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2324
2325 bfqd->wr_busy_queues++;
2326 bfqq->entity.prio_changed = 1;
2327 }
2328 if (prev != bfqq->next_rq)
2329 bfq_updated_next_req(bfqd, bfqq);
2330 }
2331
2332 /*
2333 * Assign jiffies to last_wr_start_finish in the following
2334 * cases:
2335 *
2336 * . if bfqq is not going to be weight-raised, because, for
2337 * non weight-raised queues, last_wr_start_finish stores the
2338 * arrival time of the last request; as of now, this piece
2339 * of information is used only for deciding whether to
2340 * weight-raise async queues
2341 *
2342 * . if bfqq is not weight-raised, because, if bfqq is now
2343 * switching to weight-raised, then last_wr_start_finish
2344 * stores the time when weight-raising starts
2345 *
2346 * . if bfqq is interactive, because, regardless of whether
2347 * bfqq is currently weight-raised, the weight-raising
2348 * period must start or restart (this case is considered
2349 * separately because it is not detected by the above
2350 * conditions, if bfqq is already weight-raised)
2351 *
2352 * last_wr_start_finish has to be updated also if bfqq is soft
2353 * real-time, because the weight-raising period is constantly
2354 * restarted on idle-to-busy transitions for these queues, but
2355 * this is already done in bfq_bfqq_handle_idle_busy_switch if
2356 * needed.
2357 */
2358 if (bfqd->low_latency &&
2359 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2360 bfqq->last_wr_start_finish = jiffies;
2361 }
2362
bfq_find_rq_fmerge(struct bfq_data * bfqd,struct bio * bio,struct request_queue * q)2363 static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2364 struct bio *bio,
2365 struct request_queue *q)
2366 {
2367 struct bfq_queue *bfqq = bfqd->bio_bfqq;
2368
2369
2370 if (bfqq)
2371 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2372
2373 return NULL;
2374 }
2375
get_sdist(sector_t last_pos,struct request * rq)2376 static sector_t get_sdist(sector_t last_pos, struct request *rq)
2377 {
2378 if (last_pos)
2379 return abs(blk_rq_pos(rq) - last_pos);
2380
2381 return 0;
2382 }
2383
2384 #if 0 /* Still not clear if we can do without next two functions */
2385 static void bfq_activate_request(struct request_queue *q, struct request *rq)
2386 {
2387 struct bfq_data *bfqd = q->elevator->elevator_data;
2388
2389 bfqd->rq_in_driver++;
2390 }
2391
2392 static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
2393 {
2394 struct bfq_data *bfqd = q->elevator->elevator_data;
2395
2396 bfqd->rq_in_driver--;
2397 }
2398 #endif
2399
bfq_remove_request(struct request_queue * q,struct request * rq)2400 static void bfq_remove_request(struct request_queue *q,
2401 struct request *rq)
2402 {
2403 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2404 struct bfq_data *bfqd = bfqq->bfqd;
2405 const int sync = rq_is_sync(rq);
2406
2407 if (bfqq->next_rq == rq) {
2408 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
2409 bfq_updated_next_req(bfqd, bfqq);
2410 }
2411
2412 if (rq->queuelist.prev != &rq->queuelist)
2413 list_del_init(&rq->queuelist);
2414 bfqq->queued[sync]--;
2415 /*
2416 * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2417 * may be read without holding the lock in bfq_has_work().
2418 */
2419 WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
2420 elv_rb_del(&bfqq->sort_list, rq);
2421
2422 elv_rqhash_del(q, rq);
2423 if (q->last_merge == rq)
2424 q->last_merge = NULL;
2425
2426 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2427 bfqq->next_rq = NULL;
2428
2429 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2430 bfq_del_bfqq_busy(bfqq, false);
2431 /*
2432 * bfqq emptied. In normal operation, when
2433 * bfqq is empty, bfqq->entity.service and
2434 * bfqq->entity.budget must contain,
2435 * respectively, the service received and the
2436 * budget used last time bfqq emptied. These
2437 * facts do not hold in this case, as at least
2438 * this last removal occurred while bfqq is
2439 * not in service. To avoid inconsistencies,
2440 * reset both bfqq->entity.service and
2441 * bfqq->entity.budget, if bfqq has still a
2442 * process that may issue I/O requests to it.
2443 */
2444 bfqq->entity.budget = bfqq->entity.service = 0;
2445 }
2446
2447 /*
2448 * Remove queue from request-position tree as it is empty.
2449 */
2450 if (bfqq->pos_root) {
2451 rb_erase(&bfqq->pos_node, bfqq->pos_root);
2452 bfqq->pos_root = NULL;
2453 }
2454 } else {
2455 /* see comments on bfq_pos_tree_add_move() for the unlikely() */
2456 if (unlikely(!bfqd->nonrot_with_queueing))
2457 bfq_pos_tree_add_move(bfqd, bfqq);
2458 }
2459
2460 if (rq->cmd_flags & REQ_META)
2461 bfqq->meta_pending--;
2462
2463 }
2464
bfq_bio_merge(struct request_queue * q,struct bio * bio,unsigned int nr_segs)2465 static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
2466 unsigned int nr_segs)
2467 {
2468 struct bfq_data *bfqd = q->elevator->elevator_data;
2469 struct request *free = NULL;
2470 /*
2471 * bfq_bic_lookup grabs the queue_lock: invoke it now and
2472 * store its return value for later use, to avoid nesting
2473 * queue_lock inside the bfqd->lock. We assume that the bic
2474 * returned by bfq_bic_lookup does not go away before
2475 * bfqd->lock is taken.
2476 */
2477 struct bfq_io_cq *bic = bfq_bic_lookup(q);
2478 bool ret;
2479
2480 spin_lock_irq(&bfqd->lock);
2481
2482 if (bic) {
2483 /*
2484 * Make sure cgroup info is uptodate for current process before
2485 * considering the merge.
2486 */
2487 bfq_bic_update_cgroup(bic, bio);
2488
2489 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
2490 } else {
2491 bfqd->bio_bfqq = NULL;
2492 }
2493 bfqd->bio_bic = bic;
2494
2495 ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
2496
2497 spin_unlock_irq(&bfqd->lock);
2498 if (free)
2499 blk_mq_free_request(free);
2500
2501 return ret;
2502 }
2503
bfq_request_merge(struct request_queue * q,struct request ** req,struct bio * bio)2504 static int bfq_request_merge(struct request_queue *q, struct request **req,
2505 struct bio *bio)
2506 {
2507 struct bfq_data *bfqd = q->elevator->elevator_data;
2508 struct request *__rq;
2509
2510 __rq = bfq_find_rq_fmerge(bfqd, bio, q);
2511 if (__rq && elv_bio_merge_ok(__rq, bio)) {
2512 *req = __rq;
2513
2514 if (blk_discard_mergable(__rq))
2515 return ELEVATOR_DISCARD_MERGE;
2516 return ELEVATOR_FRONT_MERGE;
2517 }
2518
2519 return ELEVATOR_NO_MERGE;
2520 }
2521
bfq_request_merged(struct request_queue * q,struct request * req,enum elv_merge type)2522 static void bfq_request_merged(struct request_queue *q, struct request *req,
2523 enum elv_merge type)
2524 {
2525 if (type == ELEVATOR_FRONT_MERGE &&
2526 rb_prev(&req->rb_node) &&
2527 blk_rq_pos(req) <
2528 blk_rq_pos(container_of(rb_prev(&req->rb_node),
2529 struct request, rb_node))) {
2530 struct bfq_queue *bfqq = RQ_BFQQ(req);
2531 struct bfq_data *bfqd;
2532 struct request *prev, *next_rq;
2533
2534 if (!bfqq)
2535 return;
2536
2537 bfqd = bfqq->bfqd;
2538
2539 /* Reposition request in its sort_list */
2540 elv_rb_del(&bfqq->sort_list, req);
2541 elv_rb_add(&bfqq->sort_list, req);
2542
2543 /* Choose next request to be served for bfqq */
2544 prev = bfqq->next_rq;
2545 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
2546 bfqd->last_position);
2547 bfqq->next_rq = next_rq;
2548 /*
2549 * If next_rq changes, update both the queue's budget to
2550 * fit the new request and the queue's position in its
2551 * rq_pos_tree.
2552 */
2553 if (prev != bfqq->next_rq) {
2554 bfq_updated_next_req(bfqd, bfqq);
2555 /*
2556 * See comments on bfq_pos_tree_add_move() for
2557 * the unlikely().
2558 */
2559 if (unlikely(!bfqd->nonrot_with_queueing))
2560 bfq_pos_tree_add_move(bfqd, bfqq);
2561 }
2562 }
2563 }
2564
2565 /*
2566 * This function is called to notify the scheduler that the requests
2567 * rq and 'next' have been merged, with 'next' going away. BFQ
2568 * exploits this hook to address the following issue: if 'next' has a
2569 * fifo_time lower that rq, then the fifo_time of rq must be set to
2570 * the value of 'next', to not forget the greater age of 'next'.
2571 *
2572 * NOTE: in this function we assume that rq is in a bfq_queue, basing
2573 * on that rq is picked from the hash table q->elevator->hash, which,
2574 * in its turn, is filled only with I/O requests present in
2575 * bfq_queues, while BFQ is in use for the request queue q. In fact,
2576 * the function that fills this hash table (elv_rqhash_add) is called
2577 * only by bfq_insert_request.
2578 */
bfq_requests_merged(struct request_queue * q,struct request * rq,struct request * next)2579 static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2580 struct request *next)
2581 {
2582 struct bfq_queue *bfqq = RQ_BFQQ(rq),
2583 *next_bfqq = RQ_BFQQ(next);
2584
2585 if (!bfqq)
2586 goto remove;
2587
2588 /*
2589 * If next and rq belong to the same bfq_queue and next is older
2590 * than rq, then reposition rq in the fifo (by substituting next
2591 * with rq). Otherwise, if next and rq belong to different
2592 * bfq_queues, never reposition rq: in fact, we would have to
2593 * reposition it with respect to next's position in its own fifo,
2594 * which would most certainly be too expensive with respect to
2595 * the benefits.
2596 */
2597 if (bfqq == next_bfqq &&
2598 !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
2599 next->fifo_time < rq->fifo_time) {
2600 list_del_init(&rq->queuelist);
2601 list_replace_init(&next->queuelist, &rq->queuelist);
2602 rq->fifo_time = next->fifo_time;
2603 }
2604
2605 if (bfqq->next_rq == next)
2606 bfqq->next_rq = rq;
2607
2608 bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
2609 remove:
2610 /* Merged request may be in the IO scheduler. Remove it. */
2611 if (!RB_EMPTY_NODE(&next->rb_node)) {
2612 bfq_remove_request(next->q, next);
2613 if (next_bfqq)
2614 bfqg_stats_update_io_remove(bfqq_group(next_bfqq),
2615 next->cmd_flags);
2616 }
2617 }
2618
2619 /* Must be called with bfqq != NULL */
bfq_bfqq_end_wr(struct bfq_queue * bfqq)2620 static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2621 {
2622 /*
2623 * If bfqq has been enjoying interactive weight-raising, then
2624 * reset soft_rt_next_start. We do it for the following
2625 * reason. bfqq may have been conveying the I/O needed to load
2626 * a soft real-time application. Such an application actually
2627 * exhibits a soft real-time I/O pattern after it finishes
2628 * loading, and finally starts doing its job. But, if bfqq has
2629 * been receiving a lot of bandwidth so far (likely to happen
2630 * on a fast device), then soft_rt_next_start now contains a
2631 * high value that. So, without this reset, bfqq would be
2632 * prevented from being possibly considered as soft_rt for a
2633 * very long time.
2634 */
2635
2636 if (bfqq->wr_cur_max_time !=
2637 bfqq->bfqd->bfq_wr_rt_max_time)
2638 bfqq->soft_rt_next_start = jiffies;
2639
2640 if (bfq_bfqq_busy(bfqq))
2641 bfqq->bfqd->wr_busy_queues--;
2642 bfqq->wr_coeff = 1;
2643 bfqq->wr_cur_max_time = 0;
2644 bfqq->last_wr_start_finish = jiffies;
2645 /*
2646 * Trigger a weight change on the next invocation of
2647 * __bfq_entity_update_weight_prio.
2648 */
2649 bfqq->entity.prio_changed = 1;
2650 }
2651
bfq_end_wr_async_queues(struct bfq_data * bfqd,struct bfq_group * bfqg)2652 void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2653 struct bfq_group *bfqg)
2654 {
2655 int i, j;
2656
2657 for (i = 0; i < 2; i++)
2658 for (j = 0; j < IOPRIO_NR_LEVELS; j++)
2659 if (bfqg->async_bfqq[i][j])
2660 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
2661 if (bfqg->async_idle_bfqq)
2662 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
2663 }
2664
bfq_end_wr(struct bfq_data * bfqd)2665 static void bfq_end_wr(struct bfq_data *bfqd)
2666 {
2667 struct bfq_queue *bfqq;
2668
2669 spin_lock_irq(&bfqd->lock);
2670
2671 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
2672 bfq_bfqq_end_wr(bfqq);
2673 list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2674 bfq_bfqq_end_wr(bfqq);
2675 bfq_end_wr_async(bfqd);
2676
2677 spin_unlock_irq(&bfqd->lock);
2678 }
2679
bfq_io_struct_pos(void * io_struct,bool request)2680 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2681 {
2682 if (request)
2683 return blk_rq_pos(io_struct);
2684 else
2685 return ((struct bio *)io_struct)->bi_iter.bi_sector;
2686 }
2687
bfq_rq_close_to_sector(void * io_struct,bool request,sector_t sector)2688 static int bfq_rq_close_to_sector(void *io_struct, bool request,
2689 sector_t sector)
2690 {
2691 return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2692 BFQQ_CLOSE_THR;
2693 }
2694
bfqq_find_close(struct bfq_data * bfqd,struct bfq_queue * bfqq,sector_t sector)2695 static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2696 struct bfq_queue *bfqq,
2697 sector_t sector)
2698 {
2699 struct rb_root *root = &bfqq_group(bfqq)->rq_pos_tree;
2700 struct rb_node *parent, *node;
2701 struct bfq_queue *__bfqq;
2702
2703 if (RB_EMPTY_ROOT(root))
2704 return NULL;
2705
2706 /*
2707 * First, if we find a request starting at the end of the last
2708 * request, choose it.
2709 */
2710 __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2711 if (__bfqq)
2712 return __bfqq;
2713
2714 /*
2715 * If the exact sector wasn't found, the parent of the NULL leaf
2716 * will contain the closest sector (rq_pos_tree sorted by
2717 * next_request position).
2718 */
2719 __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2720 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2721 return __bfqq;
2722
2723 if (blk_rq_pos(__bfqq->next_rq) < sector)
2724 node = rb_next(&__bfqq->pos_node);
2725 else
2726 node = rb_prev(&__bfqq->pos_node);
2727 if (!node)
2728 return NULL;
2729
2730 __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2731 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2732 return __bfqq;
2733
2734 return NULL;
2735 }
2736
bfq_find_close_cooperator(struct bfq_data * bfqd,struct bfq_queue * cur_bfqq,sector_t sector)2737 static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2738 struct bfq_queue *cur_bfqq,
2739 sector_t sector)
2740 {
2741 struct bfq_queue *bfqq;
2742
2743 /*
2744 * We shall notice if some of the queues are cooperating,
2745 * e.g., working closely on the same area of the device. In
2746 * that case, we can group them together and: 1) don't waste
2747 * time idling, and 2) serve the union of their requests in
2748 * the best possible order for throughput.
2749 */
2750 bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2751 if (!bfqq || bfqq == cur_bfqq)
2752 return NULL;
2753
2754 return bfqq;
2755 }
2756
2757 static struct bfq_queue *
bfq_setup_merge(struct bfq_queue * bfqq,struct bfq_queue * new_bfqq)2758 bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2759 {
2760 int process_refs, new_process_refs;
2761 struct bfq_queue *__bfqq;
2762
2763 /*
2764 * If there are no process references on the new_bfqq, then it is
2765 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2766 * may have dropped their last reference (not just their last process
2767 * reference).
2768 */
2769 if (!bfqq_process_refs(new_bfqq))
2770 return NULL;
2771
2772 /* Avoid a circular list and skip interim queue merges. */
2773 while ((__bfqq = new_bfqq->new_bfqq)) {
2774 if (__bfqq == bfqq)
2775 return NULL;
2776 new_bfqq = __bfqq;
2777 }
2778
2779 process_refs = bfqq_process_refs(bfqq);
2780 new_process_refs = bfqq_process_refs(new_bfqq);
2781 /*
2782 * If the process for the bfqq has gone away, there is no
2783 * sense in merging the queues.
2784 */
2785 if (process_refs == 0 || new_process_refs == 0)
2786 return NULL;
2787
2788 /*
2789 * Make sure merged queues belong to the same parent. Parents could
2790 * have changed since the time we decided the two queues are suitable
2791 * for merging.
2792 */
2793 if (new_bfqq->entity.parent != bfqq->entity.parent)
2794 return NULL;
2795
2796 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2797 new_bfqq->pid);
2798
2799 /*
2800 * Merging is just a redirection: the requests of the process
2801 * owning one of the two queues are redirected to the other queue.
2802 * The latter queue, in its turn, is set as shared if this is the
2803 * first time that the requests of some process are redirected to
2804 * it.
2805 *
2806 * We redirect bfqq to new_bfqq and not the opposite, because
2807 * we are in the context of the process owning bfqq, thus we
2808 * have the io_cq of this process. So we can immediately
2809 * configure this io_cq to redirect the requests of the
2810 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2811 * not available any more (new_bfqq->bic == NULL).
2812 *
2813 * Anyway, even in case new_bfqq coincides with the in-service
2814 * queue, redirecting requests the in-service queue is the
2815 * best option, as we feed the in-service queue with new
2816 * requests close to the last request served and, by doing so,
2817 * are likely to increase the throughput.
2818 */
2819 bfqq->new_bfqq = new_bfqq;
2820 /*
2821 * The above assignment schedules the following redirections:
2822 * each time some I/O for bfqq arrives, the process that
2823 * generated that I/O is disassociated from bfqq and
2824 * associated with new_bfqq. Here we increases new_bfqq->ref
2825 * in advance, adding the number of processes that are
2826 * expected to be associated with new_bfqq as they happen to
2827 * issue I/O.
2828 */
2829 new_bfqq->ref += process_refs;
2830 return new_bfqq;
2831 }
2832
bfq_may_be_close_cooperator(struct bfq_queue * bfqq,struct bfq_queue * new_bfqq)2833 static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2834 struct bfq_queue *new_bfqq)
2835 {
2836 if (bfq_too_late_for_merging(new_bfqq))
2837 return false;
2838
2839 if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2840 (bfqq->ioprio_class != new_bfqq->ioprio_class))
2841 return false;
2842
2843 /*
2844 * If either of the queues has already been detected as seeky,
2845 * then merging it with the other queue is unlikely to lead to
2846 * sequential I/O.
2847 */
2848 if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2849 return false;
2850
2851 /*
2852 * Interleaved I/O is known to be done by (some) applications
2853 * only for reads, so it does not make sense to merge async
2854 * queues.
2855 */
2856 if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2857 return false;
2858
2859 return true;
2860 }
2861
2862 static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
2863 struct bfq_queue *bfqq);
2864
2865 /*
2866 * Attempt to schedule a merge of bfqq with the currently in-service
2867 * queue or with a close queue among the scheduled queues. Return
2868 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2869 * structure otherwise.
2870 *
2871 * The OOM queue is not allowed to participate to cooperation: in fact, since
2872 * the requests temporarily redirected to the OOM queue could be redirected
2873 * again to dedicated queues at any time, the state needed to correctly
2874 * handle merging with the OOM queue would be quite complex and expensive
2875 * to maintain. Besides, in such a critical condition as an out of memory,
2876 * the benefits of queue merging may be little relevant, or even negligible.
2877 *
2878 * WARNING: queue merging may impair fairness among non-weight raised
2879 * queues, for at least two reasons: 1) the original weight of a
2880 * merged queue may change during the merged state, 2) even being the
2881 * weight the same, a merged queue may be bloated with many more
2882 * requests than the ones produced by its originally-associated
2883 * process.
2884 */
2885 static struct bfq_queue *
bfq_setup_cooperator(struct bfq_data * bfqd,struct bfq_queue * bfqq,void * io_struct,bool request,struct bfq_io_cq * bic)2886 bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2887 void *io_struct, bool request, struct bfq_io_cq *bic)
2888 {
2889 struct bfq_queue *in_service_bfqq, *new_bfqq;
2890
2891 /* if a merge has already been setup, then proceed with that first */
2892 if (bfqq->new_bfqq)
2893 return bfqq->new_bfqq;
2894
2895 /*
2896 * Check delayed stable merge for rotational or non-queueing
2897 * devs. For this branch to be executed, bfqq must not be
2898 * currently merged with some other queue (i.e., bfqq->bic
2899 * must be non null). If we considered also merged queues,
2900 * then we should also check whether bfqq has already been
2901 * merged with bic->stable_merge_bfqq. But this would be
2902 * costly and complicated.
2903 */
2904 if (unlikely(!bfqd->nonrot_with_queueing)) {
2905 /*
2906 * Make sure also that bfqq is sync, because
2907 * bic->stable_merge_bfqq may point to some queue (for
2908 * stable merging) also if bic is associated with a
2909 * sync queue, but this bfqq is async
2910 */
2911 if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq &&
2912 !bfq_bfqq_just_created(bfqq) &&
2913 time_is_before_jiffies(bfqq->split_time +
2914 msecs_to_jiffies(bfq_late_stable_merging)) &&
2915 time_is_before_jiffies(bfqq->creation_time +
2916 msecs_to_jiffies(bfq_late_stable_merging))) {
2917 struct bfq_queue *stable_merge_bfqq =
2918 bic->stable_merge_bfqq;
2919 int proc_ref = min(bfqq_process_refs(bfqq),
2920 bfqq_process_refs(stable_merge_bfqq));
2921
2922 /* deschedule stable merge, because done or aborted here */
2923 bfq_put_stable_ref(stable_merge_bfqq);
2924
2925 bic->stable_merge_bfqq = NULL;
2926
2927 if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
2928 proc_ref > 0) {
2929 /* next function will take at least one ref */
2930 struct bfq_queue *new_bfqq =
2931 bfq_setup_merge(bfqq, stable_merge_bfqq);
2932
2933 if (new_bfqq) {
2934 bic->stably_merged = true;
2935 if (new_bfqq->bic)
2936 new_bfqq->bic->stably_merged =
2937 true;
2938 }
2939 return new_bfqq;
2940 } else
2941 return NULL;
2942 }
2943 }
2944
2945 /*
2946 * Do not perform queue merging if the device is non
2947 * rotational and performs internal queueing. In fact, such a
2948 * device reaches a high speed through internal parallelism
2949 * and pipelining. This means that, to reach a high
2950 * throughput, it must have many requests enqueued at the same
2951 * time. But, in this configuration, the internal scheduling
2952 * algorithm of the device does exactly the job of queue
2953 * merging: it reorders requests so as to obtain as much as
2954 * possible a sequential I/O pattern. As a consequence, with
2955 * the workload generated by processes doing interleaved I/O,
2956 * the throughput reached by the device is likely to be the
2957 * same, with and without queue merging.
2958 *
2959 * Disabling merging also provides a remarkable benefit in
2960 * terms of throughput. Merging tends to make many workloads
2961 * artificially more uneven, because of shared queues
2962 * remaining non empty for incomparably more time than
2963 * non-merged queues. This may accentuate workload
2964 * asymmetries. For example, if one of the queues in a set of
2965 * merged queues has a higher weight than a normal queue, then
2966 * the shared queue may inherit such a high weight and, by
2967 * staying almost always active, may force BFQ to perform I/O
2968 * plugging most of the time. This evidently makes it harder
2969 * for BFQ to let the device reach a high throughput.
2970 *
2971 * Finally, the likely() macro below is not used because one
2972 * of the two branches is more likely than the other, but to
2973 * have the code path after the following if() executed as
2974 * fast as possible for the case of a non rotational device
2975 * with queueing. We want it because this is the fastest kind
2976 * of device. On the opposite end, the likely() may lengthen
2977 * the execution time of BFQ for the case of slower devices
2978 * (rotational or at least without queueing). But in this case
2979 * the execution time of BFQ matters very little, if not at
2980 * all.
2981 */
2982 if (likely(bfqd->nonrot_with_queueing))
2983 return NULL;
2984
2985 /*
2986 * Prevent bfqq from being merged if it has been created too
2987 * long ago. The idea is that true cooperating processes, and
2988 * thus their associated bfq_queues, are supposed to be
2989 * created shortly after each other. This is the case, e.g.,
2990 * for KVM/QEMU and dump I/O threads. Basing on this
2991 * assumption, the following filtering greatly reduces the
2992 * probability that two non-cooperating processes, which just
2993 * happen to do close I/O for some short time interval, have
2994 * their queues merged by mistake.
2995 */
2996 if (bfq_too_late_for_merging(bfqq))
2997 return NULL;
2998
2999 if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
3000 return NULL;
3001
3002 /* If there is only one backlogged queue, don't search. */
3003 if (bfq_tot_busy_queues(bfqd) == 1)
3004 return NULL;
3005
3006 in_service_bfqq = bfqd->in_service_queue;
3007
3008 if (in_service_bfqq && in_service_bfqq != bfqq &&
3009 likely(in_service_bfqq != &bfqd->oom_bfqq) &&
3010 bfq_rq_close_to_sector(io_struct, request,
3011 bfqd->in_serv_last_pos) &&
3012 bfqq->entity.parent == in_service_bfqq->entity.parent &&
3013 bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
3014 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
3015 if (new_bfqq)
3016 return new_bfqq;
3017 }
3018 /*
3019 * Check whether there is a cooperator among currently scheduled
3020 * queues. The only thing we need is that the bio/request is not
3021 * NULL, as we need it to establish whether a cooperator exists.
3022 */
3023 new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
3024 bfq_io_struct_pos(io_struct, request));
3025
3026 if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
3027 bfq_may_be_close_cooperator(bfqq, new_bfqq))
3028 return bfq_setup_merge(bfqq, new_bfqq);
3029
3030 return NULL;
3031 }
3032
bfq_bfqq_save_state(struct bfq_queue * bfqq)3033 static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
3034 {
3035 struct bfq_io_cq *bic = bfqq->bic;
3036
3037 /*
3038 * If !bfqq->bic, the queue is already shared or its requests
3039 * have already been redirected to a shared queue; both idle window
3040 * and weight raising state have already been saved. Do nothing.
3041 */
3042 if (!bic)
3043 return;
3044
3045 bic->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
3046 bic->saved_inject_limit = bfqq->inject_limit;
3047 bic->saved_decrease_time_jif = bfqq->decrease_time_jif;
3048
3049 bic->saved_weight = bfqq->entity.orig_weight;
3050 bic->saved_ttime = bfqq->ttime;
3051 bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
3052 bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
3053 bic->saved_io_start_time = bfqq->io_start_time;
3054 bic->saved_tot_idle_time = bfqq->tot_idle_time;
3055 bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
3056 bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
3057 if (unlikely(bfq_bfqq_just_created(bfqq) &&
3058 !bfq_bfqq_in_large_burst(bfqq) &&
3059 bfqq->bfqd->low_latency)) {
3060 /*
3061 * bfqq being merged right after being created: bfqq
3062 * would have deserved interactive weight raising, but
3063 * did not make it to be set in a weight-raised state,
3064 * because of this early merge. Store directly the
3065 * weight-raising state that would have been assigned
3066 * to bfqq, so that to avoid that bfqq unjustly fails
3067 * to enjoy weight raising if split soon.
3068 */
3069 bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
3070 bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
3071 bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
3072 bic->saved_last_wr_start_finish = jiffies;
3073 } else {
3074 bic->saved_wr_coeff = bfqq->wr_coeff;
3075 bic->saved_wr_start_at_switch_to_srt =
3076 bfqq->wr_start_at_switch_to_srt;
3077 bic->saved_service_from_wr = bfqq->service_from_wr;
3078 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
3079 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
3080 }
3081 }
3082
3083
3084 static void
bfq_reassign_last_bfqq(struct bfq_queue * cur_bfqq,struct bfq_queue * new_bfqq)3085 bfq_reassign_last_bfqq(struct bfq_queue *cur_bfqq, struct bfq_queue *new_bfqq)
3086 {
3087 if (cur_bfqq->entity.parent &&
3088 cur_bfqq->entity.parent->last_bfqq_created == cur_bfqq)
3089 cur_bfqq->entity.parent->last_bfqq_created = new_bfqq;
3090 else if (cur_bfqq->bfqd && cur_bfqq->bfqd->last_bfqq_created == cur_bfqq)
3091 cur_bfqq->bfqd->last_bfqq_created = new_bfqq;
3092 }
3093
bfq_release_process_ref(struct bfq_data * bfqd,struct bfq_queue * bfqq)3094 void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3095 {
3096 /*
3097 * To prevent bfqq's service guarantees from being violated,
3098 * bfqq may be left busy, i.e., queued for service, even if
3099 * empty (see comments in __bfq_bfqq_expire() for
3100 * details). But, if no process will send requests to bfqq any
3101 * longer, then there is no point in keeping bfqq queued for
3102 * service. In addition, keeping bfqq queued for service, but
3103 * with no process ref any longer, may have caused bfqq to be
3104 * freed when dequeued from service. But this is assumed to
3105 * never happen.
3106 */
3107 if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
3108 bfqq != bfqd->in_service_queue)
3109 bfq_del_bfqq_busy(bfqq, false);
3110
3111 bfq_reassign_last_bfqq(bfqq, NULL);
3112
3113 bfq_put_queue(bfqq);
3114 }
3115
3116 static void
bfq_merge_bfqqs(struct bfq_data * bfqd,struct bfq_io_cq * bic,struct bfq_queue * bfqq,struct bfq_queue * new_bfqq)3117 bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
3118 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
3119 {
3120 bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
3121 (unsigned long)new_bfqq->pid);
3122 /* Save weight raising and idle window of the merged queues */
3123 bfq_bfqq_save_state(bfqq);
3124 bfq_bfqq_save_state(new_bfqq);
3125 if (bfq_bfqq_IO_bound(bfqq))
3126 bfq_mark_bfqq_IO_bound(new_bfqq);
3127 bfq_clear_bfqq_IO_bound(bfqq);
3128
3129 /*
3130 * The processes associated with bfqq are cooperators of the
3131 * processes associated with new_bfqq. So, if bfqq has a
3132 * waker, then assume that all these processes will be happy
3133 * to let bfqq's waker freely inject I/O when they have no
3134 * I/O.
3135 */
3136 if (bfqq->waker_bfqq && !new_bfqq->waker_bfqq &&
3137 bfqq->waker_bfqq != new_bfqq) {
3138 new_bfqq->waker_bfqq = bfqq->waker_bfqq;
3139 new_bfqq->tentative_waker_bfqq = NULL;
3140
3141 /*
3142 * If the waker queue disappears, then
3143 * new_bfqq->waker_bfqq must be reset. So insert
3144 * new_bfqq into the woken_list of the waker. See
3145 * bfq_check_waker for details.
3146 */
3147 hlist_add_head(&new_bfqq->woken_list_node,
3148 &new_bfqq->waker_bfqq->woken_list);
3149
3150 }
3151
3152 /*
3153 * If bfqq is weight-raised, then let new_bfqq inherit
3154 * weight-raising. To reduce false positives, neglect the case
3155 * where bfqq has just been created, but has not yet made it
3156 * to be weight-raised (which may happen because EQM may merge
3157 * bfqq even before bfq_add_request is executed for the first
3158 * time for bfqq). Handling this case would however be very
3159 * easy, thanks to the flag just_created.
3160 */
3161 if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
3162 new_bfqq->wr_coeff = bfqq->wr_coeff;
3163 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
3164 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
3165 new_bfqq->wr_start_at_switch_to_srt =
3166 bfqq->wr_start_at_switch_to_srt;
3167 if (bfq_bfqq_busy(new_bfqq))
3168 bfqd->wr_busy_queues++;
3169 new_bfqq->entity.prio_changed = 1;
3170 }
3171
3172 if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
3173 bfqq->wr_coeff = 1;
3174 bfqq->entity.prio_changed = 1;
3175 if (bfq_bfqq_busy(bfqq))
3176 bfqd->wr_busy_queues--;
3177 }
3178
3179 bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
3180 bfqd->wr_busy_queues);
3181
3182 /*
3183 * Merge queues (that is, let bic redirect its requests to new_bfqq)
3184 */
3185 bic_set_bfqq(bic, new_bfqq, true);
3186 bfq_mark_bfqq_coop(new_bfqq);
3187 /*
3188 * new_bfqq now belongs to at least two bics (it is a shared queue):
3189 * set new_bfqq->bic to NULL. bfqq either:
3190 * - does not belong to any bic any more, and hence bfqq->bic must
3191 * be set to NULL, or
3192 * - is a queue whose owning bics have already been redirected to a
3193 * different queue, hence the queue is destined to not belong to
3194 * any bic soon and bfqq->bic is already NULL (therefore the next
3195 * assignment causes no harm).
3196 */
3197 new_bfqq->bic = NULL;
3198 /*
3199 * If the queue is shared, the pid is the pid of one of the associated
3200 * processes. Which pid depends on the exact sequence of merge events
3201 * the queue underwent. So printing such a pid is useless and confusing
3202 * because it reports a random pid between those of the associated
3203 * processes.
3204 * We mark such a queue with a pid -1, and then print SHARED instead of
3205 * a pid in logging messages.
3206 */
3207 new_bfqq->pid = -1;
3208 bfqq->bic = NULL;
3209
3210 bfq_reassign_last_bfqq(bfqq, new_bfqq);
3211
3212 bfq_release_process_ref(bfqd, bfqq);
3213 }
3214
bfq_allow_bio_merge(struct request_queue * q,struct request * rq,struct bio * bio)3215 static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
3216 struct bio *bio)
3217 {
3218 struct bfq_data *bfqd = q->elevator->elevator_data;
3219 bool is_sync = op_is_sync(bio->bi_opf);
3220 struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
3221
3222 /*
3223 * Disallow merge of a sync bio into an async request.
3224 */
3225 if (is_sync && !rq_is_sync(rq))
3226 return false;
3227
3228 /*
3229 * Lookup the bfqq that this bio will be queued with. Allow
3230 * merge only if rq is queued there.
3231 */
3232 if (!bfqq)
3233 return false;
3234
3235 /*
3236 * We take advantage of this function to perform an early merge
3237 * of the queues of possible cooperating processes.
3238 */
3239 new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false, bfqd->bio_bic);
3240 if (new_bfqq) {
3241 /*
3242 * bic still points to bfqq, then it has not yet been
3243 * redirected to some other bfq_queue, and a queue
3244 * merge between bfqq and new_bfqq can be safely
3245 * fulfilled, i.e., bic can be redirected to new_bfqq
3246 * and bfqq can be put.
3247 */
3248 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
3249 new_bfqq);
3250 /*
3251 * If we get here, bio will be queued into new_queue,
3252 * so use new_bfqq to decide whether bio and rq can be
3253 * merged.
3254 */
3255 bfqq = new_bfqq;
3256
3257 /*
3258 * Change also bqfd->bio_bfqq, as
3259 * bfqd->bio_bic now points to new_bfqq, and
3260 * this function may be invoked again (and then may
3261 * use again bqfd->bio_bfqq).
3262 */
3263 bfqd->bio_bfqq = bfqq;
3264 }
3265
3266 return bfqq == RQ_BFQQ(rq);
3267 }
3268
3269 /*
3270 * Set the maximum time for the in-service queue to consume its
3271 * budget. This prevents seeky processes from lowering the throughput.
3272 * In practice, a time-slice service scheme is used with seeky
3273 * processes.
3274 */
bfq_set_budget_timeout(struct bfq_data * bfqd,struct bfq_queue * bfqq)3275 static void bfq_set_budget_timeout(struct bfq_data *bfqd,
3276 struct bfq_queue *bfqq)
3277 {
3278 unsigned int timeout_coeff;
3279
3280 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
3281 timeout_coeff = 1;
3282 else
3283 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
3284
3285 bfqd->last_budget_start = ktime_get();
3286
3287 bfqq->budget_timeout = jiffies +
3288 bfqd->bfq_timeout * timeout_coeff;
3289 }
3290
__bfq_set_in_service_queue(struct bfq_data * bfqd,struct bfq_queue * bfqq)3291 static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
3292 struct bfq_queue *bfqq)
3293 {
3294 if (bfqq) {
3295 bfq_clear_bfqq_fifo_expire(bfqq);
3296
3297 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
3298
3299 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
3300 bfqq->wr_coeff > 1 &&
3301 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
3302 time_is_before_jiffies(bfqq->budget_timeout)) {
3303 /*
3304 * For soft real-time queues, move the start
3305 * of the weight-raising period forward by the
3306 * time the queue has not received any
3307 * service. Otherwise, a relatively long
3308 * service delay is likely to cause the
3309 * weight-raising period of the queue to end,
3310 * because of the short duration of the
3311 * weight-raising period of a soft real-time
3312 * queue. It is worth noting that this move
3313 * is not so dangerous for the other queues,
3314 * because soft real-time queues are not
3315 * greedy.
3316 *
3317 * To not add a further variable, we use the
3318 * overloaded field budget_timeout to
3319 * determine for how long the queue has not
3320 * received service, i.e., how much time has
3321 * elapsed since the queue expired. However,
3322 * this is a little imprecise, because
3323 * budget_timeout is set to jiffies if bfqq
3324 * not only expires, but also remains with no
3325 * request.
3326 */
3327 if (time_after(bfqq->budget_timeout,
3328 bfqq->last_wr_start_finish))
3329 bfqq->last_wr_start_finish +=
3330 jiffies - bfqq->budget_timeout;
3331 else
3332 bfqq->last_wr_start_finish = jiffies;
3333 }
3334
3335 bfq_set_budget_timeout(bfqd, bfqq);
3336 bfq_log_bfqq(bfqd, bfqq,
3337 "set_in_service_queue, cur-budget = %d",
3338 bfqq->entity.budget);
3339 }
3340
3341 bfqd->in_service_queue = bfqq;
3342 bfqd->in_serv_last_pos = 0;
3343 }
3344
3345 /*
3346 * Get and set a new queue for service.
3347 */
bfq_set_in_service_queue(struct bfq_data * bfqd)3348 static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
3349 {
3350 struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
3351
3352 __bfq_set_in_service_queue(bfqd, bfqq);
3353 return bfqq;
3354 }
3355
bfq_arm_slice_timer(struct bfq_data * bfqd)3356 static void bfq_arm_slice_timer(struct bfq_data *bfqd)
3357 {
3358 struct bfq_queue *bfqq = bfqd->in_service_queue;
3359 u32 sl;
3360
3361 bfq_mark_bfqq_wait_request(bfqq);
3362
3363 /*
3364 * We don't want to idle for seeks, but we do want to allow
3365 * fair distribution of slice time for a process doing back-to-back
3366 * seeks. So allow a little bit of time for him to submit a new rq.
3367 */
3368 sl = bfqd->bfq_slice_idle;
3369 /*
3370 * Unless the queue is being weight-raised or the scenario is
3371 * asymmetric, grant only minimum idle time if the queue
3372 * is seeky. A long idling is preserved for a weight-raised
3373 * queue, or, more in general, in an asymmetric scenario,
3374 * because a long idling is needed for guaranteeing to a queue
3375 * its reserved share of the throughput (in particular, it is
3376 * needed if the queue has a higher weight than some other
3377 * queue).
3378 */
3379 if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
3380 !bfq_asymmetric_scenario(bfqd, bfqq))
3381 sl = min_t(u64, sl, BFQ_MIN_TT);
3382 else if (bfqq->wr_coeff > 1)
3383 sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
3384
3385 bfqd->last_idling_start = ktime_get();
3386 bfqd->last_idling_start_jiffies = jiffies;
3387
3388 hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
3389 HRTIMER_MODE_REL);
3390 bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
3391 }
3392
3393 /*
3394 * In autotuning mode, max_budget is dynamically recomputed as the
3395 * amount of sectors transferred in timeout at the estimated peak
3396 * rate. This enables BFQ to utilize a full timeslice with a full
3397 * budget, even if the in-service queue is served at peak rate. And
3398 * this maximises throughput with sequential workloads.
3399 */
bfq_calc_max_budget(struct bfq_data * bfqd)3400 static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
3401 {
3402 return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3403 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3404 }
3405
3406 /*
3407 * Update parameters related to throughput and responsiveness, as a
3408 * function of the estimated peak rate. See comments on
3409 * bfq_calc_max_budget(), and on the ref_wr_duration array.
3410 */
update_thr_responsiveness_params(struct bfq_data * bfqd)3411 static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3412 {
3413 if (bfqd->bfq_user_max_budget == 0) {
3414 bfqd->bfq_max_budget =
3415 bfq_calc_max_budget(bfqd);
3416 bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3417 }
3418 }
3419
bfq_reset_rate_computation(struct bfq_data * bfqd,struct request * rq)3420 static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3421 struct request *rq)
3422 {
3423 if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3424 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
3425 bfqd->peak_rate_samples = 1;
3426 bfqd->sequential_samples = 0;
3427 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3428 blk_rq_sectors(rq);
3429 } else /* no new rq dispatched, just reset the number of samples */
3430 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3431
3432 bfq_log(bfqd,
3433 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
3434 bfqd->peak_rate_samples, bfqd->sequential_samples,
3435 bfqd->tot_sectors_dispatched);
3436 }
3437
bfq_update_rate_reset(struct bfq_data * bfqd,struct request * rq)3438 static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3439 {
3440 u32 rate, weight, divisor;
3441
3442 /*
3443 * For the convergence property to hold (see comments on
3444 * bfq_update_peak_rate()) and for the assessment to be
3445 * reliable, a minimum number of samples must be present, and
3446 * a minimum amount of time must have elapsed. If not so, do
3447 * not compute new rate. Just reset parameters, to get ready
3448 * for a new evaluation attempt.
3449 */
3450 if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3451 bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3452 goto reset_computation;
3453
3454 /*
3455 * If a new request completion has occurred after last
3456 * dispatch, then, to approximate the rate at which requests
3457 * have been served by the device, it is more precise to
3458 * extend the observation interval to the last completion.
3459 */
3460 bfqd->delta_from_first =
3461 max_t(u64, bfqd->delta_from_first,
3462 bfqd->last_completion - bfqd->first_dispatch);
3463
3464 /*
3465 * Rate computed in sects/usec, and not sects/nsec, for
3466 * precision issues.
3467 */
3468 rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3469 div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3470
3471 /*
3472 * Peak rate not updated if:
3473 * - the percentage of sequential dispatches is below 3/4 of the
3474 * total, and rate is below the current estimated peak rate
3475 * - rate is unreasonably high (> 20M sectors/sec)
3476 */
3477 if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3478 rate <= bfqd->peak_rate) ||
3479 rate > 20<<BFQ_RATE_SHIFT)
3480 goto reset_computation;
3481
3482 /*
3483 * We have to update the peak rate, at last! To this purpose,
3484 * we use a low-pass filter. We compute the smoothing constant
3485 * of the filter as a function of the 'weight' of the new
3486 * measured rate.
3487 *
3488 * As can be seen in next formulas, we define this weight as a
3489 * quantity proportional to how sequential the workload is,
3490 * and to how long the observation time interval is.
3491 *
3492 * The weight runs from 0 to 8. The maximum value of the
3493 * weight, 8, yields the minimum value for the smoothing
3494 * constant. At this minimum value for the smoothing constant,
3495 * the measured rate contributes for half of the next value of
3496 * the estimated peak rate.
3497 *
3498 * So, the first step is to compute the weight as a function
3499 * of how sequential the workload is. Note that the weight
3500 * cannot reach 9, because bfqd->sequential_samples cannot
3501 * become equal to bfqd->peak_rate_samples, which, in its
3502 * turn, holds true because bfqd->sequential_samples is not
3503 * incremented for the first sample.
3504 */
3505 weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3506
3507 /*
3508 * Second step: further refine the weight as a function of the
3509 * duration of the observation interval.
3510 */
3511 weight = min_t(u32, 8,
3512 div_u64(weight * bfqd->delta_from_first,
3513 BFQ_RATE_REF_INTERVAL));
3514
3515 /*
3516 * Divisor ranging from 10, for minimum weight, to 2, for
3517 * maximum weight.
3518 */
3519 divisor = 10 - weight;
3520
3521 /*
3522 * Finally, update peak rate:
3523 *
3524 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
3525 */
3526 bfqd->peak_rate *= divisor-1;
3527 bfqd->peak_rate /= divisor;
3528 rate /= divisor; /* smoothing constant alpha = 1/divisor */
3529
3530 bfqd->peak_rate += rate;
3531
3532 /*
3533 * For a very slow device, bfqd->peak_rate can reach 0 (see
3534 * the minimum representable values reported in the comments
3535 * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3536 * divisions by zero where bfqd->peak_rate is used as a
3537 * divisor.
3538 */
3539 bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3540
3541 update_thr_responsiveness_params(bfqd);
3542
3543 reset_computation:
3544 bfq_reset_rate_computation(bfqd, rq);
3545 }
3546
3547 /*
3548 * Update the read/write peak rate (the main quantity used for
3549 * auto-tuning, see update_thr_responsiveness_params()).
3550 *
3551 * It is not trivial to estimate the peak rate (correctly): because of
3552 * the presence of sw and hw queues between the scheduler and the
3553 * device components that finally serve I/O requests, it is hard to
3554 * say exactly when a given dispatched request is served inside the
3555 * device, and for how long. As a consequence, it is hard to know
3556 * precisely at what rate a given set of requests is actually served
3557 * by the device.
3558 *
3559 * On the opposite end, the dispatch time of any request is trivially
3560 * available, and, from this piece of information, the "dispatch rate"
3561 * of requests can be immediately computed. So, the idea in the next
3562 * function is to use what is known, namely request dispatch times
3563 * (plus, when useful, request completion times), to estimate what is
3564 * unknown, namely in-device request service rate.
3565 *
3566 * The main issue is that, because of the above facts, the rate at
3567 * which a certain set of requests is dispatched over a certain time
3568 * interval can vary greatly with respect to the rate at which the
3569 * same requests are then served. But, since the size of any
3570 * intermediate queue is limited, and the service scheme is lossless
3571 * (no request is silently dropped), the following obvious convergence
3572 * property holds: the number of requests dispatched MUST become
3573 * closer and closer to the number of requests completed as the
3574 * observation interval grows. This is the key property used in
3575 * the next function to estimate the peak service rate as a function
3576 * of the observed dispatch rate. The function assumes to be invoked
3577 * on every request dispatch.
3578 */
bfq_update_peak_rate(struct bfq_data * bfqd,struct request * rq)3579 static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3580 {
3581 u64 now_ns = ktime_get_ns();
3582
3583 if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3584 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3585 bfqd->peak_rate_samples);
3586 bfq_reset_rate_computation(bfqd, rq);
3587 goto update_last_values; /* will add one sample */
3588 }
3589
3590 /*
3591 * Device idle for very long: the observation interval lasting
3592 * up to this dispatch cannot be a valid observation interval
3593 * for computing a new peak rate (similarly to the late-
3594 * completion event in bfq_completed_request()). Go to
3595 * update_rate_and_reset to have the following three steps
3596 * taken:
3597 * - close the observation interval at the last (previous)
3598 * request dispatch or completion
3599 * - compute rate, if possible, for that observation interval
3600 * - start a new observation interval with this dispatch
3601 */
3602 if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3603 bfqd->rq_in_driver == 0)
3604 goto update_rate_and_reset;
3605
3606 /* Update sampling information */
3607 bfqd->peak_rate_samples++;
3608
3609 if ((bfqd->rq_in_driver > 0 ||
3610 now_ns - bfqd->last_completion < BFQ_MIN_TT)
3611 && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3612 bfqd->sequential_samples++;
3613
3614 bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3615
3616 /* Reset max observed rq size every 32 dispatches */
3617 if (likely(bfqd->peak_rate_samples % 32))
3618 bfqd->last_rq_max_size =
3619 max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3620 else
3621 bfqd->last_rq_max_size = blk_rq_sectors(rq);
3622
3623 bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3624
3625 /* Target observation interval not yet reached, go on sampling */
3626 if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3627 goto update_last_values;
3628
3629 update_rate_and_reset:
3630 bfq_update_rate_reset(bfqd, rq);
3631 update_last_values:
3632 bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3633 if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3634 bfqd->in_serv_last_pos = bfqd->last_position;
3635 bfqd->last_dispatch = now_ns;
3636 }
3637
3638 /*
3639 * Remove request from internal lists.
3640 */
bfq_dispatch_remove(struct request_queue * q,struct request * rq)3641 static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3642 {
3643 struct bfq_queue *bfqq = RQ_BFQQ(rq);
3644
3645 /*
3646 * For consistency, the next instruction should have been
3647 * executed after removing the request from the queue and
3648 * dispatching it. We execute instead this instruction before
3649 * bfq_remove_request() (and hence introduce a temporary
3650 * inconsistency), for efficiency. In fact, should this
3651 * dispatch occur for a non in-service bfqq, this anticipated
3652 * increment prevents two counters related to bfqq->dispatched
3653 * from risking to be, first, uselessly decremented, and then
3654 * incremented again when the (new) value of bfqq->dispatched
3655 * happens to be taken into account.
3656 */
3657 bfqq->dispatched++;
3658 bfq_update_peak_rate(q->elevator->elevator_data, rq);
3659
3660 bfq_remove_request(q, rq);
3661 }
3662
3663 /*
3664 * There is a case where idling does not have to be performed for
3665 * throughput concerns, but to preserve the throughput share of
3666 * the process associated with bfqq.
3667 *
3668 * To introduce this case, we can note that allowing the drive
3669 * to enqueue more than one request at a time, and hence
3670 * delegating de facto final scheduling decisions to the
3671 * drive's internal scheduler, entails loss of control on the
3672 * actual request service order. In particular, the critical
3673 * situation is when requests from different processes happen
3674 * to be present, at the same time, in the internal queue(s)
3675 * of the drive. In such a situation, the drive, by deciding
3676 * the service order of the internally-queued requests, does
3677 * determine also the actual throughput distribution among
3678 * these processes. But the drive typically has no notion or
3679 * concern about per-process throughput distribution, and
3680 * makes its decisions only on a per-request basis. Therefore,
3681 * the service distribution enforced by the drive's internal
3682 * scheduler is likely to coincide with the desired throughput
3683 * distribution only in a completely symmetric, or favorably
3684 * skewed scenario where:
3685 * (i-a) each of these processes must get the same throughput as
3686 * the others,
3687 * (i-b) in case (i-a) does not hold, it holds that the process
3688 * associated with bfqq must receive a lower or equal
3689 * throughput than any of the other processes;
3690 * (ii) the I/O of each process has the same properties, in
3691 * terms of locality (sequential or random), direction
3692 * (reads or writes), request sizes, greediness
3693 * (from I/O-bound to sporadic), and so on;
3694
3695 * In fact, in such a scenario, the drive tends to treat the requests
3696 * of each process in about the same way as the requests of the
3697 * others, and thus to provide each of these processes with about the
3698 * same throughput. This is exactly the desired throughput
3699 * distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3700 * even more convenient distribution for (the process associated with)
3701 * bfqq.
3702 *
3703 * In contrast, in any asymmetric or unfavorable scenario, device
3704 * idling (I/O-dispatch plugging) is certainly needed to guarantee
3705 * that bfqq receives its assigned fraction of the device throughput
3706 * (see [1] for details).
3707 *
3708 * The problem is that idling may significantly reduce throughput with
3709 * certain combinations of types of I/O and devices. An important
3710 * example is sync random I/O on flash storage with command
3711 * queueing. So, unless bfqq falls in cases where idling also boosts
3712 * throughput, it is important to check conditions (i-a), i(-b) and
3713 * (ii) accurately, so as to avoid idling when not strictly needed for
3714 * service guarantees.
3715 *
3716 * Unfortunately, it is extremely difficult to thoroughly check
3717 * condition (ii). And, in case there are active groups, it becomes
3718 * very difficult to check conditions (i-a) and (i-b) too. In fact,
3719 * if there are active groups, then, for conditions (i-a) or (i-b) to
3720 * become false 'indirectly', it is enough that an active group
3721 * contains more active processes or sub-groups than some other active
3722 * group. More precisely, for conditions (i-a) or (i-b) to become
3723 * false because of such a group, it is not even necessary that the
3724 * group is (still) active: it is sufficient that, even if the group
3725 * has become inactive, some of its descendant processes still have
3726 * some request already dispatched but still waiting for
3727 * completion. In fact, requests have still to be guaranteed their
3728 * share of the throughput even after being dispatched. In this
3729 * respect, it is easy to show that, if a group frequently becomes
3730 * inactive while still having in-flight requests, and if, when this
3731 * happens, the group is not considered in the calculation of whether
3732 * the scenario is asymmetric, then the group may fail to be
3733 * guaranteed its fair share of the throughput (basically because
3734 * idling may not be performed for the descendant processes of the
3735 * group, but it had to be). We address this issue with the following
3736 * bi-modal behavior, implemented in the function
3737 * bfq_asymmetric_scenario().
3738 *
3739 * If there are groups with requests waiting for completion
3740 * (as commented above, some of these groups may even be
3741 * already inactive), then the scenario is tagged as
3742 * asymmetric, conservatively, without checking any of the
3743 * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3744 * This behavior matches also the fact that groups are created
3745 * exactly if controlling I/O is a primary concern (to
3746 * preserve bandwidth and latency guarantees).
3747 *
3748 * On the opposite end, if there are no groups with requests waiting
3749 * for completion, then only conditions (i-a) and (i-b) are actually
3750 * controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3751 * idling is not performed, regardless of whether condition (ii)
3752 * holds. In other words, only if conditions (i-a) and (i-b) do not
3753 * hold, then idling is allowed, and the device tends to be prevented
3754 * from queueing many requests, possibly of several processes. Since
3755 * there are no groups with requests waiting for completion, then, to
3756 * control conditions (i-a) and (i-b) it is enough to check just
3757 * whether all the queues with requests waiting for completion also
3758 * have the same weight.
3759 *
3760 * Not checking condition (ii) evidently exposes bfqq to the
3761 * risk of getting less throughput than its fair share.
3762 * However, for queues with the same weight, a further
3763 * mechanism, preemption, mitigates or even eliminates this
3764 * problem. And it does so without consequences on overall
3765 * throughput. This mechanism and its benefits are explained
3766 * in the next three paragraphs.
3767 *
3768 * Even if a queue, say Q, is expired when it remains idle, Q
3769 * can still preempt the new in-service queue if the next
3770 * request of Q arrives soon (see the comments on
3771 * bfq_bfqq_update_budg_for_activation). If all queues and
3772 * groups have the same weight, this form of preemption,
3773 * combined with the hole-recovery heuristic described in the
3774 * comments on function bfq_bfqq_update_budg_for_activation,
3775 * are enough to preserve a correct bandwidth distribution in
3776 * the mid term, even without idling. In fact, even if not
3777 * idling allows the internal queues of the device to contain
3778 * many requests, and thus to reorder requests, we can rather
3779 * safely assume that the internal scheduler still preserves a
3780 * minimum of mid-term fairness.
3781 *
3782 * More precisely, this preemption-based, idleless approach
3783 * provides fairness in terms of IOPS, and not sectors per
3784 * second. This can be seen with a simple example. Suppose
3785 * that there are two queues with the same weight, but that
3786 * the first queue receives requests of 8 sectors, while the
3787 * second queue receives requests of 1024 sectors. In
3788 * addition, suppose that each of the two queues contains at
3789 * most one request at a time, which implies that each queue
3790 * always remains idle after it is served. Finally, after
3791 * remaining idle, each queue receives very quickly a new
3792 * request. It follows that the two queues are served
3793 * alternatively, preempting each other if needed. This
3794 * implies that, although both queues have the same weight,
3795 * the queue with large requests receives a service that is
3796 * 1024/8 times as high as the service received by the other
3797 * queue.
3798 *
3799 * The motivation for using preemption instead of idling (for
3800 * queues with the same weight) is that, by not idling,
3801 * service guarantees are preserved (completely or at least in
3802 * part) without minimally sacrificing throughput. And, if
3803 * there is no active group, then the primary expectation for
3804 * this device is probably a high throughput.
3805 *
3806 * We are now left only with explaining the two sub-conditions in the
3807 * additional compound condition that is checked below for deciding
3808 * whether the scenario is asymmetric. To explain the first
3809 * sub-condition, we need to add that the function
3810 * bfq_asymmetric_scenario checks the weights of only
3811 * non-weight-raised queues, for efficiency reasons (see comments on
3812 * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3813 * is checked explicitly here. More precisely, the compound condition
3814 * below takes into account also the fact that, even if bfqq is being
3815 * weight-raised, the scenario is still symmetric if all queues with
3816 * requests waiting for completion happen to be
3817 * weight-raised. Actually, we should be even more precise here, and
3818 * differentiate between interactive weight raising and soft real-time
3819 * weight raising.
3820 *
3821 * The second sub-condition checked in the compound condition is
3822 * whether there is a fair amount of already in-flight I/O not
3823 * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3824 * following reason. The drive may decide to serve in-flight
3825 * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3826 * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3827 * I/O-dispatching is not plugged, then, while bfqq remains empty, a
3828 * basically uncontrolled amount of I/O from other queues may be
3829 * dispatched too, possibly causing the service of bfqq's I/O to be
3830 * delayed even longer in the drive. This problem gets more and more
3831 * serious as the speed and the queue depth of the drive grow,
3832 * because, as these two quantities grow, the probability to find no
3833 * queue busy but many requests in flight grows too. By contrast,
3834 * plugging I/O dispatching minimizes the delay induced by already
3835 * in-flight I/O, and enables bfqq to recover the bandwidth it may
3836 * lose because of this delay.
3837 *
3838 * As a side note, it is worth considering that the above
3839 * device-idling countermeasures may however fail in the following
3840 * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3841 * in a time period during which all symmetry sub-conditions hold, and
3842 * therefore the device is allowed to enqueue many requests, but at
3843 * some later point in time some sub-condition stops to hold, then it
3844 * may become impossible to make requests be served in the desired
3845 * order until all the requests already queued in the device have been
3846 * served. The last sub-condition commented above somewhat mitigates
3847 * this problem for weight-raised queues.
3848 *
3849 * However, as an additional mitigation for this problem, we preserve
3850 * plugging for a special symmetric case that may suddenly turn into
3851 * asymmetric: the case where only bfqq is busy. In this case, not
3852 * expiring bfqq does not cause any harm to any other queues in terms
3853 * of service guarantees. In contrast, it avoids the following unlucky
3854 * sequence of events: (1) bfqq is expired, (2) a new queue with a
3855 * lower weight than bfqq becomes busy (or more queues), (3) the new
3856 * queue is served until a new request arrives for bfqq, (4) when bfqq
3857 * is finally served, there are so many requests of the new queue in
3858 * the drive that the pending requests for bfqq take a lot of time to
3859 * be served. In particular, event (2) may case even already
3860 * dispatched requests of bfqq to be delayed, inside the drive. So, to
3861 * avoid this series of events, the scenario is preventively declared
3862 * as asymmetric also if bfqq is the only busy queues
3863 */
idling_needed_for_service_guarantees(struct bfq_data * bfqd,struct bfq_queue * bfqq)3864 static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3865 struct bfq_queue *bfqq)
3866 {
3867 int tot_busy_queues = bfq_tot_busy_queues(bfqd);
3868
3869 /* No point in idling for bfqq if it won't get requests any longer */
3870 if (unlikely(!bfqq_process_refs(bfqq)))
3871 return false;
3872
3873 return (bfqq->wr_coeff > 1 &&
3874 (bfqd->wr_busy_queues <
3875 tot_busy_queues ||
3876 bfqd->rq_in_driver >=
3877 bfqq->dispatched + 4)) ||
3878 bfq_asymmetric_scenario(bfqd, bfqq) ||
3879 tot_busy_queues == 1;
3880 }
3881
__bfq_bfqq_expire(struct bfq_data * bfqd,struct bfq_queue * bfqq,enum bfqq_expiration reason)3882 static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3883 enum bfqq_expiration reason)
3884 {
3885 /*
3886 * If this bfqq is shared between multiple processes, check
3887 * to make sure that those processes are still issuing I/Os
3888 * within the mean seek distance. If not, it may be time to
3889 * break the queues apart again.
3890 */
3891 if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3892 bfq_mark_bfqq_split_coop(bfqq);
3893
3894 /*
3895 * Consider queues with a higher finish virtual time than
3896 * bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3897 * true, then bfqq's bandwidth would be violated if an
3898 * uncontrolled amount of I/O from these queues were
3899 * dispatched while bfqq is waiting for its new I/O to
3900 * arrive. This is exactly what may happen if this is a forced
3901 * expiration caused by a preemption attempt, and if bfqq is
3902 * not re-scheduled. To prevent this from happening, re-queue
3903 * bfqq if it needs I/O-dispatch plugging, even if it is
3904 * empty. By doing so, bfqq is granted to be served before the
3905 * above queues (provided that bfqq is of course eligible).
3906 */
3907 if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3908 !(reason == BFQQE_PREEMPTED &&
3909 idling_needed_for_service_guarantees(bfqd, bfqq))) {
3910 if (bfqq->dispatched == 0)
3911 /*
3912 * Overloading budget_timeout field to store
3913 * the time at which the queue remains with no
3914 * backlog and no outstanding request; used by
3915 * the weight-raising mechanism.
3916 */
3917 bfqq->budget_timeout = jiffies;
3918
3919 bfq_del_bfqq_busy(bfqq, true);
3920 } else {
3921 bfq_requeue_bfqq(bfqd, bfqq, true);
3922 /*
3923 * Resort priority tree of potential close cooperators.
3924 * See comments on bfq_pos_tree_add_move() for the unlikely().
3925 */
3926 if (unlikely(!bfqd->nonrot_with_queueing &&
3927 !RB_EMPTY_ROOT(&bfqq->sort_list)))
3928 bfq_pos_tree_add_move(bfqd, bfqq);
3929 }
3930
3931 /*
3932 * All in-service entities must have been properly deactivated
3933 * or requeued before executing the next function, which
3934 * resets all in-service entities as no more in service. This
3935 * may cause bfqq to be freed. If this happens, the next
3936 * function returns true.
3937 */
3938 return __bfq_bfqd_reset_in_service(bfqd);
3939 }
3940
3941 /**
3942 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3943 * @bfqd: device data.
3944 * @bfqq: queue to update.
3945 * @reason: reason for expiration.
3946 *
3947 * Handle the feedback on @bfqq budget at queue expiration.
3948 * See the body for detailed comments.
3949 */
__bfq_bfqq_recalc_budget(struct bfq_data * bfqd,struct bfq_queue * bfqq,enum bfqq_expiration reason)3950 static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3951 struct bfq_queue *bfqq,
3952 enum bfqq_expiration reason)
3953 {
3954 struct request *next_rq;
3955 int budget, min_budget;
3956
3957 min_budget = bfq_min_budget(bfqd);
3958
3959 if (bfqq->wr_coeff == 1)
3960 budget = bfqq->max_budget;
3961 else /*
3962 * Use a constant, low budget for weight-raised queues,
3963 * to help achieve a low latency. Keep it slightly higher
3964 * than the minimum possible budget, to cause a little
3965 * bit fewer expirations.
3966 */
3967 budget = 2 * min_budget;
3968
3969 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3970 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3971 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3972 budget, bfq_min_budget(bfqd));
3973 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3974 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3975
3976 if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3977 switch (reason) {
3978 /*
3979 * Caveat: in all the following cases we trade latency
3980 * for throughput.
3981 */
3982 case BFQQE_TOO_IDLE:
3983 /*
3984 * This is the only case where we may reduce
3985 * the budget: if there is no request of the
3986 * process still waiting for completion, then
3987 * we assume (tentatively) that the timer has
3988 * expired because the batch of requests of
3989 * the process could have been served with a
3990 * smaller budget. Hence, betting that
3991 * process will behave in the same way when it
3992 * becomes backlogged again, we reduce its
3993 * next budget. As long as we guess right,
3994 * this budget cut reduces the latency
3995 * experienced by the process.
3996 *
3997 * However, if there are still outstanding
3998 * requests, then the process may have not yet
3999 * issued its next request just because it is
4000 * still waiting for the completion of some of
4001 * the still outstanding ones. So in this
4002 * subcase we do not reduce its budget, on the
4003 * contrary we increase it to possibly boost
4004 * the throughput, as discussed in the
4005 * comments to the BUDGET_TIMEOUT case.
4006 */
4007 if (bfqq->dispatched > 0) /* still outstanding reqs */
4008 budget = min(budget * 2, bfqd->bfq_max_budget);
4009 else {
4010 if (budget > 5 * min_budget)
4011 budget -= 4 * min_budget;
4012 else
4013 budget = min_budget;
4014 }
4015 break;
4016 case BFQQE_BUDGET_TIMEOUT:
4017 /*
4018 * We double the budget here because it gives
4019 * the chance to boost the throughput if this
4020 * is not a seeky process (and has bumped into
4021 * this timeout because of, e.g., ZBR).
4022 */
4023 budget = min(budget * 2, bfqd->bfq_max_budget);
4024 break;
4025 case BFQQE_BUDGET_EXHAUSTED:
4026 /*
4027 * The process still has backlog, and did not
4028 * let either the budget timeout or the disk
4029 * idling timeout expire. Hence it is not
4030 * seeky, has a short thinktime and may be
4031 * happy with a higher budget too. So
4032 * definitely increase the budget of this good
4033 * candidate to boost the disk throughput.
4034 */
4035 budget = min(budget * 4, bfqd->bfq_max_budget);
4036 break;
4037 case BFQQE_NO_MORE_REQUESTS:
4038 /*
4039 * For queues that expire for this reason, it
4040 * is particularly important to keep the
4041 * budget close to the actual service they
4042 * need. Doing so reduces the timestamp
4043 * misalignment problem described in the
4044 * comments in the body of
4045 * __bfq_activate_entity. In fact, suppose
4046 * that a queue systematically expires for
4047 * BFQQE_NO_MORE_REQUESTS and presents a
4048 * new request in time to enjoy timestamp
4049 * back-shifting. The larger the budget of the
4050 * queue is with respect to the service the
4051 * queue actually requests in each service
4052 * slot, the more times the queue can be
4053 * reactivated with the same virtual finish
4054 * time. It follows that, even if this finish
4055 * time is pushed to the system virtual time
4056 * to reduce the consequent timestamp
4057 * misalignment, the queue unjustly enjoys for
4058 * many re-activations a lower finish time
4059 * than all newly activated queues.
4060 *
4061 * The service needed by bfqq is measured
4062 * quite precisely by bfqq->entity.service.
4063 * Since bfqq does not enjoy device idling,
4064 * bfqq->entity.service is equal to the number
4065 * of sectors that the process associated with
4066 * bfqq requested to read/write before waiting
4067 * for request completions, or blocking for
4068 * other reasons.
4069 */
4070 budget = max_t(int, bfqq->entity.service, min_budget);
4071 break;
4072 default:
4073 return;
4074 }
4075 } else if (!bfq_bfqq_sync(bfqq)) {
4076 /*
4077 * Async queues get always the maximum possible
4078 * budget, as for them we do not care about latency
4079 * (in addition, their ability to dispatch is limited
4080 * by the charging factor).
4081 */
4082 budget = bfqd->bfq_max_budget;
4083 }
4084
4085 bfqq->max_budget = budget;
4086
4087 if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
4088 !bfqd->bfq_user_max_budget)
4089 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
4090
4091 /*
4092 * If there is still backlog, then assign a new budget, making
4093 * sure that it is large enough for the next request. Since
4094 * the finish time of bfqq must be kept in sync with the
4095 * budget, be sure to call __bfq_bfqq_expire() *after* this
4096 * update.
4097 *
4098 * If there is no backlog, then no need to update the budget;
4099 * it will be updated on the arrival of a new request.
4100 */
4101 next_rq = bfqq->next_rq;
4102 if (next_rq)
4103 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
4104 bfq_serv_to_charge(next_rq, bfqq));
4105
4106 bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
4107 next_rq ? blk_rq_sectors(next_rq) : 0,
4108 bfqq->entity.budget);
4109 }
4110
4111 /*
4112 * Return true if the process associated with bfqq is "slow". The slow
4113 * flag is used, in addition to the budget timeout, to reduce the
4114 * amount of service provided to seeky processes, and thus reduce
4115 * their chances to lower the throughput. More details in the comments
4116 * on the function bfq_bfqq_expire().
4117 *
4118 * An important observation is in order: as discussed in the comments
4119 * on the function bfq_update_peak_rate(), with devices with internal
4120 * queues, it is hard if ever possible to know when and for how long
4121 * an I/O request is processed by the device (apart from the trivial
4122 * I/O pattern where a new request is dispatched only after the
4123 * previous one has been completed). This makes it hard to evaluate
4124 * the real rate at which the I/O requests of each bfq_queue are
4125 * served. In fact, for an I/O scheduler like BFQ, serving a
4126 * bfq_queue means just dispatching its requests during its service
4127 * slot (i.e., until the budget of the queue is exhausted, or the
4128 * queue remains idle, or, finally, a timeout fires). But, during the
4129 * service slot of a bfq_queue, around 100 ms at most, the device may
4130 * be even still processing requests of bfq_queues served in previous
4131 * service slots. On the opposite end, the requests of the in-service
4132 * bfq_queue may be completed after the service slot of the queue
4133 * finishes.
4134 *
4135 * Anyway, unless more sophisticated solutions are used
4136 * (where possible), the sum of the sizes of the requests dispatched
4137 * during the service slot of a bfq_queue is probably the only
4138 * approximation available for the service received by the bfq_queue
4139 * during its service slot. And this sum is the quantity used in this
4140 * function to evaluate the I/O speed of a process.
4141 */
bfq_bfqq_is_slow(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool compensate,enum bfqq_expiration reason,unsigned long * delta_ms)4142 static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4143 bool compensate, enum bfqq_expiration reason,
4144 unsigned long *delta_ms)
4145 {
4146 ktime_t delta_ktime;
4147 u32 delta_usecs;
4148 bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
4149
4150 if (!bfq_bfqq_sync(bfqq))
4151 return false;
4152
4153 if (compensate)
4154 delta_ktime = bfqd->last_idling_start;
4155 else
4156 delta_ktime = ktime_get();
4157 delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
4158 delta_usecs = ktime_to_us(delta_ktime);
4159
4160 /* don't use too short time intervals */
4161 if (delta_usecs < 1000) {
4162 if (blk_queue_nonrot(bfqd->queue))
4163 /*
4164 * give same worst-case guarantees as idling
4165 * for seeky
4166 */
4167 *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
4168 else /* charge at least one seek */
4169 *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
4170
4171 return slow;
4172 }
4173
4174 *delta_ms = delta_usecs / USEC_PER_MSEC;
4175
4176 /*
4177 * Use only long (> 20ms) intervals to filter out excessive
4178 * spikes in service rate estimation.
4179 */
4180 if (delta_usecs > 20000) {
4181 /*
4182 * Caveat for rotational devices: processes doing I/O
4183 * in the slower disk zones tend to be slow(er) even
4184 * if not seeky. In this respect, the estimated peak
4185 * rate is likely to be an average over the disk
4186 * surface. Accordingly, to not be too harsh with
4187 * unlucky processes, a process is deemed slow only if
4188 * its rate has been lower than half of the estimated
4189 * peak rate.
4190 */
4191 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
4192 }
4193
4194 bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
4195
4196 return slow;
4197 }
4198
4199 /*
4200 * To be deemed as soft real-time, an application must meet two
4201 * requirements. First, the application must not require an average
4202 * bandwidth higher than the approximate bandwidth required to playback or
4203 * record a compressed high-definition video.
4204 * The next function is invoked on the completion of the last request of a
4205 * batch, to compute the next-start time instant, soft_rt_next_start, such
4206 * that, if the next request of the application does not arrive before
4207 * soft_rt_next_start, then the above requirement on the bandwidth is met.
4208 *
4209 * The second requirement is that the request pattern of the application is
4210 * isochronous, i.e., that, after issuing a request or a batch of requests,
4211 * the application stops issuing new requests until all its pending requests
4212 * have been completed. After that, the application may issue a new batch,
4213 * and so on.
4214 * For this reason the next function is invoked to compute
4215 * soft_rt_next_start only for applications that meet this requirement,
4216 * whereas soft_rt_next_start is set to infinity for applications that do
4217 * not.
4218 *
4219 * Unfortunately, even a greedy (i.e., I/O-bound) application may
4220 * happen to meet, occasionally or systematically, both the above
4221 * bandwidth and isochrony requirements. This may happen at least in
4222 * the following circumstances. First, if the CPU load is high. The
4223 * application may stop issuing requests while the CPUs are busy
4224 * serving other processes, then restart, then stop again for a while,
4225 * and so on. The other circumstances are related to the storage
4226 * device: the storage device is highly loaded or reaches a low-enough
4227 * throughput with the I/O of the application (e.g., because the I/O
4228 * is random and/or the device is slow). In all these cases, the
4229 * I/O of the application may be simply slowed down enough to meet
4230 * the bandwidth and isochrony requirements. To reduce the probability
4231 * that greedy applications are deemed as soft real-time in these
4232 * corner cases, a further rule is used in the computation of
4233 * soft_rt_next_start: the return value of this function is forced to
4234 * be higher than the maximum between the following two quantities.
4235 *
4236 * (a) Current time plus: (1) the maximum time for which the arrival
4237 * of a request is waited for when a sync queue becomes idle,
4238 * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
4239 * postpone for a moment the reason for adding a few extra
4240 * jiffies; we get back to it after next item (b). Lower-bounding
4241 * the return value of this function with the current time plus
4242 * bfqd->bfq_slice_idle tends to filter out greedy applications,
4243 * because the latter issue their next request as soon as possible
4244 * after the last one has been completed. In contrast, a soft
4245 * real-time application spends some time processing data, after a
4246 * batch of its requests has been completed.
4247 *
4248 * (b) Current value of bfqq->soft_rt_next_start. As pointed out
4249 * above, greedy applications may happen to meet both the
4250 * bandwidth and isochrony requirements under heavy CPU or
4251 * storage-device load. In more detail, in these scenarios, these
4252 * applications happen, only for limited time periods, to do I/O
4253 * slowly enough to meet all the requirements described so far,
4254 * including the filtering in above item (a). These slow-speed
4255 * time intervals are usually interspersed between other time
4256 * intervals during which these applications do I/O at a very high
4257 * speed. Fortunately, exactly because of the high speed of the
4258 * I/O in the high-speed intervals, the values returned by this
4259 * function happen to be so high, near the end of any such
4260 * high-speed interval, to be likely to fall *after* the end of
4261 * the low-speed time interval that follows. These high values are
4262 * stored in bfqq->soft_rt_next_start after each invocation of
4263 * this function. As a consequence, if the last value of
4264 * bfqq->soft_rt_next_start is constantly used to lower-bound the
4265 * next value that this function may return, then, from the very
4266 * beginning of a low-speed interval, bfqq->soft_rt_next_start is
4267 * likely to be constantly kept so high that any I/O request
4268 * issued during the low-speed interval is considered as arriving
4269 * to soon for the application to be deemed as soft
4270 * real-time. Then, in the high-speed interval that follows, the
4271 * application will not be deemed as soft real-time, just because
4272 * it will do I/O at a high speed. And so on.
4273 *
4274 * Getting back to the filtering in item (a), in the following two
4275 * cases this filtering might be easily passed by a greedy
4276 * application, if the reference quantity was just
4277 * bfqd->bfq_slice_idle:
4278 * 1) HZ is so low that the duration of a jiffy is comparable to or
4279 * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
4280 * devices with HZ=100. The time granularity may be so coarse
4281 * that the approximation, in jiffies, of bfqd->bfq_slice_idle
4282 * is rather lower than the exact value.
4283 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
4284 * for a while, then suddenly 'jump' by several units to recover the lost
4285 * increments. This seems to happen, e.g., inside virtual machines.
4286 * To address this issue, in the filtering in (a) we do not use as a
4287 * reference time interval just bfqd->bfq_slice_idle, but
4288 * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
4289 * minimum number of jiffies for which the filter seems to be quite
4290 * precise also in embedded systems and KVM/QEMU virtual machines.
4291 */
bfq_bfqq_softrt_next_start(struct bfq_data * bfqd,struct bfq_queue * bfqq)4292 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
4293 struct bfq_queue *bfqq)
4294 {
4295 return max3(bfqq->soft_rt_next_start,
4296 bfqq->last_idle_bklogged +
4297 HZ * bfqq->service_from_backlogged /
4298 bfqd->bfq_wr_max_softrt_rate,
4299 jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
4300 }
4301
4302 /**
4303 * bfq_bfqq_expire - expire a queue.
4304 * @bfqd: device owning the queue.
4305 * @bfqq: the queue to expire.
4306 * @compensate: if true, compensate for the time spent idling.
4307 * @reason: the reason causing the expiration.
4308 *
4309 * If the process associated with bfqq does slow I/O (e.g., because it
4310 * issues random requests), we charge bfqq with the time it has been
4311 * in service instead of the service it has received (see
4312 * bfq_bfqq_charge_time for details on how this goal is achieved). As
4313 * a consequence, bfqq will typically get higher timestamps upon
4314 * reactivation, and hence it will be rescheduled as if it had
4315 * received more service than what it has actually received. In the
4316 * end, bfqq receives less service in proportion to how slowly its
4317 * associated process consumes its budgets (and hence how seriously it
4318 * tends to lower the throughput). In addition, this time-charging
4319 * strategy guarantees time fairness among slow processes. In
4320 * contrast, if the process associated with bfqq is not slow, we
4321 * charge bfqq exactly with the service it has received.
4322 *
4323 * Charging time to the first type of queues and the exact service to
4324 * the other has the effect of using the WF2Q+ policy to schedule the
4325 * former on a timeslice basis, without violating service domain
4326 * guarantees among the latter.
4327 */
bfq_bfqq_expire(struct bfq_data * bfqd,struct bfq_queue * bfqq,bool compensate,enum bfqq_expiration reason)4328 void bfq_bfqq_expire(struct bfq_data *bfqd,
4329 struct bfq_queue *bfqq,
4330 bool compensate,
4331 enum bfqq_expiration reason)
4332 {
4333 bool slow;
4334 unsigned long delta = 0;
4335 struct bfq_entity *entity = &bfqq->entity;
4336
4337 /*
4338 * Check whether the process is slow (see bfq_bfqq_is_slow).
4339 */
4340 slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
4341
4342 /*
4343 * As above explained, charge slow (typically seeky) and
4344 * timed-out queues with the time and not the service
4345 * received, to favor sequential workloads.
4346 *
4347 * Processes doing I/O in the slower disk zones will tend to
4348 * be slow(er) even if not seeky. Therefore, since the
4349 * estimated peak rate is actually an average over the disk
4350 * surface, these processes may timeout just for bad luck. To
4351 * avoid punishing them, do not charge time to processes that
4352 * succeeded in consuming at least 2/3 of their budget. This
4353 * allows BFQ to preserve enough elasticity to still perform
4354 * bandwidth, and not time, distribution with little unlucky
4355 * or quasi-sequential processes.
4356 */
4357 if (bfqq->wr_coeff == 1 &&
4358 (slow ||
4359 (reason == BFQQE_BUDGET_TIMEOUT &&
4360 bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
4361 bfq_bfqq_charge_time(bfqd, bfqq, delta);
4362
4363 if (bfqd->low_latency && bfqq->wr_coeff == 1)
4364 bfqq->last_wr_start_finish = jiffies;
4365
4366 if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
4367 RB_EMPTY_ROOT(&bfqq->sort_list)) {
4368 /*
4369 * If we get here, and there are no outstanding
4370 * requests, then the request pattern is isochronous
4371 * (see the comments on the function
4372 * bfq_bfqq_softrt_next_start()). Therefore we can
4373 * compute soft_rt_next_start.
4374 *
4375 * If, instead, the queue still has outstanding
4376 * requests, then we have to wait for the completion
4377 * of all the outstanding requests to discover whether
4378 * the request pattern is actually isochronous.
4379 */
4380 if (bfqq->dispatched == 0)
4381 bfqq->soft_rt_next_start =
4382 bfq_bfqq_softrt_next_start(bfqd, bfqq);
4383 else if (bfqq->dispatched > 0) {
4384 /*
4385 * Schedule an update of soft_rt_next_start to when
4386 * the task may be discovered to be isochronous.
4387 */
4388 bfq_mark_bfqq_softrt_update(bfqq);
4389 }
4390 }
4391
4392 bfq_log_bfqq(bfqd, bfqq,
4393 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
4394 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
4395
4396 /*
4397 * bfqq expired, so no total service time needs to be computed
4398 * any longer: reset state machine for measuring total service
4399 * times.
4400 */
4401 bfqd->rqs_injected = bfqd->wait_dispatch = false;
4402 bfqd->waited_rq = NULL;
4403
4404 /*
4405 * Increase, decrease or leave budget unchanged according to
4406 * reason.
4407 */
4408 __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4409 if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4410 /* bfqq is gone, no more actions on it */
4411 return;
4412
4413 /* mark bfqq as waiting a request only if a bic still points to it */
4414 if (!bfq_bfqq_busy(bfqq) &&
4415 reason != BFQQE_BUDGET_TIMEOUT &&
4416 reason != BFQQE_BUDGET_EXHAUSTED) {
4417 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4418 /*
4419 * Not setting service to 0, because, if the next rq
4420 * arrives in time, the queue will go on receiving
4421 * service with this same budget (as if it never expired)
4422 */
4423 } else
4424 entity->service = 0;
4425
4426 /*
4427 * Reset the received-service counter for every parent entity.
4428 * Differently from what happens with bfqq->entity.service,
4429 * the resetting of this counter never needs to be postponed
4430 * for parent entities. In fact, in case bfqq may have a
4431 * chance to go on being served using the last, partially
4432 * consumed budget, bfqq->entity.service needs to be kept,
4433 * because if bfqq then actually goes on being served using
4434 * the same budget, the last value of bfqq->entity.service is
4435 * needed to properly decrement bfqq->entity.budget by the
4436 * portion already consumed. In contrast, it is not necessary
4437 * to keep entity->service for parent entities too, because
4438 * the bubble up of the new value of bfqq->entity.budget will
4439 * make sure that the budgets of parent entities are correct,
4440 * even in case bfqq and thus parent entities go on receiving
4441 * service with the same budget.
4442 */
4443 entity = entity->parent;
4444 for_each_entity(entity)
4445 entity->service = 0;
4446 }
4447
4448 /*
4449 * Budget timeout is not implemented through a dedicated timer, but
4450 * just checked on request arrivals and completions, as well as on
4451 * idle timer expirations.
4452 */
bfq_bfqq_budget_timeout(struct bfq_queue * bfqq)4453 static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4454 {
4455 return time_is_before_eq_jiffies(bfqq->budget_timeout);
4456 }
4457
4458 /*
4459 * If we expire a queue that is actively waiting (i.e., with the
4460 * device idled) for the arrival of a new request, then we may incur
4461 * the timestamp misalignment problem described in the body of the
4462 * function __bfq_activate_entity. Hence we return true only if this
4463 * condition does not hold, or if the queue is slow enough to deserve
4464 * only to be kicked off for preserving a high throughput.
4465 */
bfq_may_expire_for_budg_timeout(struct bfq_queue * bfqq)4466 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4467 {
4468 bfq_log_bfqq(bfqq->bfqd, bfqq,
4469 "may_budget_timeout: wait_request %d left %d timeout %d",
4470 bfq_bfqq_wait_request(bfqq),
4471 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
4472 bfq_bfqq_budget_timeout(bfqq));
4473
4474 return (!bfq_bfqq_wait_request(bfqq) ||
4475 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
4476 &&
4477 bfq_bfqq_budget_timeout(bfqq);
4478 }
4479
idling_boosts_thr_without_issues(struct bfq_data * bfqd,struct bfq_queue * bfqq)4480 static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4481 struct bfq_queue *bfqq)
4482 {
4483 bool rot_without_queueing =
4484 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4485 bfqq_sequential_and_IO_bound,
4486 idling_boosts_thr;
4487
4488 /* No point in idling for bfqq if it won't get requests any longer */
4489 if (unlikely(!bfqq_process_refs(bfqq)))
4490 return false;
4491
4492 bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4493 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4494
4495 /*
4496 * The next variable takes into account the cases where idling
4497 * boosts the throughput.
4498 *
4499 * The value of the variable is computed considering, first, that
4500 * idling is virtually always beneficial for the throughput if:
4501 * (a) the device is not NCQ-capable and rotational, or
4502 * (b) regardless of the presence of NCQ, the device is rotational and
4503 * the request pattern for bfqq is I/O-bound and sequential, or
4504 * (c) regardless of whether it is rotational, the device is
4505 * not NCQ-capable and the request pattern for bfqq is
4506 * I/O-bound and sequential.
4507 *
4508 * Secondly, and in contrast to the above item (b), idling an
4509 * NCQ-capable flash-based device would not boost the
4510 * throughput even with sequential I/O; rather it would lower
4511 * the throughput in proportion to how fast the device
4512 * is. Accordingly, the next variable is true if any of the
4513 * above conditions (a), (b) or (c) is true, and, in
4514 * particular, happens to be false if bfqd is an NCQ-capable
4515 * flash-based device.
4516 */
4517 idling_boosts_thr = rot_without_queueing ||
4518 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4519 bfqq_sequential_and_IO_bound);
4520
4521 /*
4522 * The return value of this function is equal to that of
4523 * idling_boosts_thr, unless a special case holds. In this
4524 * special case, described below, idling may cause problems to
4525 * weight-raised queues.
4526 *
4527 * When the request pool is saturated (e.g., in the presence
4528 * of write hogs), if the processes associated with
4529 * non-weight-raised queues ask for requests at a lower rate,
4530 * then processes associated with weight-raised queues have a
4531 * higher probability to get a request from the pool
4532 * immediately (or at least soon) when they need one. Thus
4533 * they have a higher probability to actually get a fraction
4534 * of the device throughput proportional to their high
4535 * weight. This is especially true with NCQ-capable drives,
4536 * which enqueue several requests in advance, and further
4537 * reorder internally-queued requests.
4538 *
4539 * For this reason, we force to false the return value if
4540 * there are weight-raised busy queues. In this case, and if
4541 * bfqq is not weight-raised, this guarantees that the device
4542 * is not idled for bfqq (if, instead, bfqq is weight-raised,
4543 * then idling will be guaranteed by another variable, see
4544 * below). Combined with the timestamping rules of BFQ (see
4545 * [1] for details), this behavior causes bfqq, and hence any
4546 * sync non-weight-raised queue, to get a lower number of
4547 * requests served, and thus to ask for a lower number of
4548 * requests from the request pool, before the busy
4549 * weight-raised queues get served again. This often mitigates
4550 * starvation problems in the presence of heavy write
4551 * workloads and NCQ, thereby guaranteeing a higher
4552 * application and system responsiveness in these hostile
4553 * scenarios.
4554 */
4555 return idling_boosts_thr &&
4556 bfqd->wr_busy_queues == 0;
4557 }
4558
4559 /*
4560 * For a queue that becomes empty, device idling is allowed only if
4561 * this function returns true for that queue. As a consequence, since
4562 * device idling plays a critical role for both throughput boosting
4563 * and service guarantees, the return value of this function plays a
4564 * critical role as well.
4565 *
4566 * In a nutshell, this function returns true only if idling is
4567 * beneficial for throughput or, even if detrimental for throughput,
4568 * idling is however necessary to preserve service guarantees (low
4569 * latency, desired throughput distribution, ...). In particular, on
4570 * NCQ-capable devices, this function tries to return false, so as to
4571 * help keep the drives' internal queues full, whenever this helps the
4572 * device boost the throughput without causing any service-guarantee
4573 * issue.
4574 *
4575 * Most of the issues taken into account to get the return value of
4576 * this function are not trivial. We discuss these issues in the two
4577 * functions providing the main pieces of information needed by this
4578 * function.
4579 */
bfq_better_to_idle(struct bfq_queue * bfqq)4580 static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4581 {
4582 struct bfq_data *bfqd = bfqq->bfqd;
4583 bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4584
4585 /* No point in idling for bfqq if it won't get requests any longer */
4586 if (unlikely(!bfqq_process_refs(bfqq)))
4587 return false;
4588
4589 if (unlikely(bfqd->strict_guarantees))
4590 return true;
4591
4592 /*
4593 * Idling is performed only if slice_idle > 0. In addition, we
4594 * do not idle if
4595 * (a) bfqq is async
4596 * (b) bfqq is in the idle io prio class: in this case we do
4597 * not idle because we want to minimize the bandwidth that
4598 * queues in this class can steal to higher-priority queues
4599 */
4600 if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4601 bfq_class_idle(bfqq))
4602 return false;
4603
4604 idling_boosts_thr_with_no_issue =
4605 idling_boosts_thr_without_issues(bfqd, bfqq);
4606
4607 idling_needed_for_service_guar =
4608 idling_needed_for_service_guarantees(bfqd, bfqq);
4609
4610 /*
4611 * We have now the two components we need to compute the
4612 * return value of the function, which is true only if idling
4613 * either boosts the throughput (without issues), or is
4614 * necessary to preserve service guarantees.
4615 */
4616 return idling_boosts_thr_with_no_issue ||
4617 idling_needed_for_service_guar;
4618 }
4619
4620 /*
4621 * If the in-service queue is empty but the function bfq_better_to_idle
4622 * returns true, then:
4623 * 1) the queue must remain in service and cannot be expired, and
4624 * 2) the device must be idled to wait for the possible arrival of a new
4625 * request for the queue.
4626 * See the comments on the function bfq_better_to_idle for the reasons
4627 * why performing device idling is the best choice to boost the throughput
4628 * and preserve service guarantees when bfq_better_to_idle itself
4629 * returns true.
4630 */
bfq_bfqq_must_idle(struct bfq_queue * bfqq)4631 static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4632 {
4633 return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4634 }
4635
4636 /*
4637 * This function chooses the queue from which to pick the next extra
4638 * I/O request to inject, if it finds a compatible queue. See the
4639 * comments on bfq_update_inject_limit() for details on the injection
4640 * mechanism, and for the definitions of the quantities mentioned
4641 * below.
4642 */
4643 static struct bfq_queue *
bfq_choose_bfqq_for_injection(struct bfq_data * bfqd)4644 bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4645 {
4646 struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4647 unsigned int limit = in_serv_bfqq->inject_limit;
4648 /*
4649 * If
4650 * - bfqq is not weight-raised and therefore does not carry
4651 * time-critical I/O,
4652 * or
4653 * - regardless of whether bfqq is weight-raised, bfqq has
4654 * however a long think time, during which it can absorb the
4655 * effect of an appropriate number of extra I/O requests
4656 * from other queues (see bfq_update_inject_limit for
4657 * details on the computation of this number);
4658 * then injection can be performed without restrictions.
4659 */
4660 bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4661 !bfq_bfqq_has_short_ttime(in_serv_bfqq);
4662
4663 /*
4664 * If
4665 * - the baseline total service time could not be sampled yet,
4666 * so the inject limit happens to be still 0, and
4667 * - a lot of time has elapsed since the plugging of I/O
4668 * dispatching started, so drive speed is being wasted
4669 * significantly;
4670 * then temporarily raise inject limit to one request.
4671 */
4672 if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4673 bfq_bfqq_wait_request(in_serv_bfqq) &&
4674 time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4675 bfqd->bfq_slice_idle)
4676 )
4677 limit = 1;
4678
4679 if (bfqd->rq_in_driver >= limit)
4680 return NULL;
4681
4682 /*
4683 * Linear search of the source queue for injection; but, with
4684 * a high probability, very few steps are needed to find a
4685 * candidate queue, i.e., a queue with enough budget left for
4686 * its next request. In fact:
4687 * - BFQ dynamically updates the budget of every queue so as
4688 * to accommodate the expected backlog of the queue;
4689 * - if a queue gets all its requests dispatched as injected
4690 * service, then the queue is removed from the active list
4691 * (and re-added only if it gets new requests, but then it
4692 * is assigned again enough budget for its new backlog).
4693 */
4694 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
4695 if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4696 (in_serv_always_inject || bfqq->wr_coeff > 1) &&
4697 bfq_serv_to_charge(bfqq->next_rq, bfqq) <=
4698 bfq_bfqq_budget_left(bfqq)) {
4699 /*
4700 * Allow for only one large in-flight request
4701 * on non-rotational devices, for the
4702 * following reason. On non-rotationl drives,
4703 * large requests take much longer than
4704 * smaller requests to be served. In addition,
4705 * the drive prefers to serve large requests
4706 * w.r.t. to small ones, if it can choose. So,
4707 * having more than one large requests queued
4708 * in the drive may easily make the next first
4709 * request of the in-service queue wait for so
4710 * long to break bfqq's service guarantees. On
4711 * the bright side, large requests let the
4712 * drive reach a very high throughput, even if
4713 * there is only one in-flight large request
4714 * at a time.
4715 */
4716 if (blk_queue_nonrot(bfqd->queue) &&
4717 blk_rq_sectors(bfqq->next_rq) >=
4718 BFQQ_SECT_THR_NONROT)
4719 limit = min_t(unsigned int, 1, limit);
4720 else
4721 limit = in_serv_bfqq->inject_limit;
4722
4723 if (bfqd->rq_in_driver < limit) {
4724 bfqd->rqs_injected = true;
4725 return bfqq;
4726 }
4727 }
4728
4729 return NULL;
4730 }
4731
4732 /*
4733 * Select a queue for service. If we have a current queue in service,
4734 * check whether to continue servicing it, or retrieve and set a new one.
4735 */
bfq_select_queue(struct bfq_data * bfqd)4736 static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4737 {
4738 struct bfq_queue *bfqq;
4739 struct request *next_rq;
4740 enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4741
4742 bfqq = bfqd->in_service_queue;
4743 if (!bfqq)
4744 goto new_queue;
4745
4746 bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4747
4748 /*
4749 * Do not expire bfqq for budget timeout if bfqq may be about
4750 * to enjoy device idling. The reason why, in this case, we
4751 * prevent bfqq from expiring is the same as in the comments
4752 * on the case where bfq_bfqq_must_idle() returns true, in
4753 * bfq_completed_request().
4754 */
4755 if (bfq_may_expire_for_budg_timeout(bfqq) &&
4756 !bfq_bfqq_must_idle(bfqq))
4757 goto expire;
4758
4759 check_queue:
4760 /*
4761 * This loop is rarely executed more than once. Even when it
4762 * happens, it is much more convenient to re-execute this loop
4763 * than to return NULL and trigger a new dispatch to get a
4764 * request served.
4765 */
4766 next_rq = bfqq->next_rq;
4767 /*
4768 * If bfqq has requests queued and it has enough budget left to
4769 * serve them, keep the queue, otherwise expire it.
4770 */
4771 if (next_rq) {
4772 if (bfq_serv_to_charge(next_rq, bfqq) >
4773 bfq_bfqq_budget_left(bfqq)) {
4774 /*
4775 * Expire the queue for budget exhaustion,
4776 * which makes sure that the next budget is
4777 * enough to serve the next request, even if
4778 * it comes from the fifo expired path.
4779 */
4780 reason = BFQQE_BUDGET_EXHAUSTED;
4781 goto expire;
4782 } else {
4783 /*
4784 * The idle timer may be pending because we may
4785 * not disable disk idling even when a new request
4786 * arrives.
4787 */
4788 if (bfq_bfqq_wait_request(bfqq)) {
4789 /*
4790 * If we get here: 1) at least a new request
4791 * has arrived but we have not disabled the
4792 * timer because the request was too small,
4793 * 2) then the block layer has unplugged
4794 * the device, causing the dispatch to be
4795 * invoked.
4796 *
4797 * Since the device is unplugged, now the
4798 * requests are probably large enough to
4799 * provide a reasonable throughput.
4800 * So we disable idling.
4801 */
4802 bfq_clear_bfqq_wait_request(bfqq);
4803 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4804 }
4805 goto keep_queue;
4806 }
4807 }
4808
4809 /*
4810 * No requests pending. However, if the in-service queue is idling
4811 * for a new request, or has requests waiting for a completion and
4812 * may idle after their completion, then keep it anyway.
4813 *
4814 * Yet, inject service from other queues if it boosts
4815 * throughput and is possible.
4816 */
4817 if (bfq_bfqq_wait_request(bfqq) ||
4818 (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4819 struct bfq_queue *async_bfqq =
4820 bfqq->bic && bfqq->bic->bfqq[0] &&
4821 bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
4822 bfqq->bic->bfqq[0]->next_rq ?
4823 bfqq->bic->bfqq[0] : NULL;
4824 struct bfq_queue *blocked_bfqq =
4825 !hlist_empty(&bfqq->woken_list) ?
4826 container_of(bfqq->woken_list.first,
4827 struct bfq_queue,
4828 woken_list_node)
4829 : NULL;
4830
4831 /*
4832 * The next four mutually-exclusive ifs decide
4833 * whether to try injection, and choose the queue to
4834 * pick an I/O request from.
4835 *
4836 * The first if checks whether the process associated
4837 * with bfqq has also async I/O pending. If so, it
4838 * injects such I/O unconditionally. Injecting async
4839 * I/O from the same process can cause no harm to the
4840 * process. On the contrary, it can only increase
4841 * bandwidth and reduce latency for the process.
4842 *
4843 * The second if checks whether there happens to be a
4844 * non-empty waker queue for bfqq, i.e., a queue whose
4845 * I/O needs to be completed for bfqq to receive new
4846 * I/O. This happens, e.g., if bfqq is associated with
4847 * a process that does some sync. A sync generates
4848 * extra blocking I/O, which must be completed before
4849 * the process associated with bfqq can go on with its
4850 * I/O. If the I/O of the waker queue is not served,
4851 * then bfqq remains empty, and no I/O is dispatched,
4852 * until the idle timeout fires for bfqq. This is
4853 * likely to result in lower bandwidth and higher
4854 * latencies for bfqq, and in a severe loss of total
4855 * throughput. The best action to take is therefore to
4856 * serve the waker queue as soon as possible. So do it
4857 * (without relying on the third alternative below for
4858 * eventually serving waker_bfqq's I/O; see the last
4859 * paragraph for further details). This systematic
4860 * injection of I/O from the waker queue does not
4861 * cause any delay to bfqq's I/O. On the contrary,
4862 * next bfqq's I/O is brought forward dramatically,
4863 * for it is not blocked for milliseconds.
4864 *
4865 * The third if checks whether there is a queue woken
4866 * by bfqq, and currently with pending I/O. Such a
4867 * woken queue does not steal bandwidth from bfqq,
4868 * because it remains soon without I/O if bfqq is not
4869 * served. So there is virtually no risk of loss of
4870 * bandwidth for bfqq if this woken queue has I/O
4871 * dispatched while bfqq is waiting for new I/O.
4872 *
4873 * The fourth if checks whether bfqq is a queue for
4874 * which it is better to avoid injection. It is so if
4875 * bfqq delivers more throughput when served without
4876 * any further I/O from other queues in the middle, or
4877 * if the service times of bfqq's I/O requests both
4878 * count more than overall throughput, and may be
4879 * easily increased by injection (this happens if bfqq
4880 * has a short think time). If none of these
4881 * conditions holds, then a candidate queue for
4882 * injection is looked for through
4883 * bfq_choose_bfqq_for_injection(). Note that the
4884 * latter may return NULL (for example if the inject
4885 * limit for bfqq is currently 0).
4886 *
4887 * NOTE: motivation for the second alternative
4888 *
4889 * Thanks to the way the inject limit is updated in
4890 * bfq_update_has_short_ttime(), it is rather likely
4891 * that, if I/O is being plugged for bfqq and the
4892 * waker queue has pending I/O requests that are
4893 * blocking bfqq's I/O, then the fourth alternative
4894 * above lets the waker queue get served before the
4895 * I/O-plugging timeout fires. So one may deem the
4896 * second alternative superfluous. It is not, because
4897 * the fourth alternative may be way less effective in
4898 * case of a synchronization. For two main
4899 * reasons. First, throughput may be low because the
4900 * inject limit may be too low to guarantee the same
4901 * amount of injected I/O, from the waker queue or
4902 * other queues, that the second alternative
4903 * guarantees (the second alternative unconditionally
4904 * injects a pending I/O request of the waker queue
4905 * for each bfq_dispatch_request()). Second, with the
4906 * fourth alternative, the duration of the plugging,
4907 * i.e., the time before bfqq finally receives new I/O,
4908 * may not be minimized, because the waker queue may
4909 * happen to be served only after other queues.
4910 */
4911 if (async_bfqq &&
4912 icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4913 bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
4914 bfq_bfqq_budget_left(async_bfqq))
4915 bfqq = bfqq->bic->bfqq[0];
4916 else if (bfqq->waker_bfqq &&
4917 bfq_bfqq_busy(bfqq->waker_bfqq) &&
4918 bfqq->waker_bfqq->next_rq &&
4919 bfq_serv_to_charge(bfqq->waker_bfqq->next_rq,
4920 bfqq->waker_bfqq) <=
4921 bfq_bfqq_budget_left(bfqq->waker_bfqq)
4922 )
4923 bfqq = bfqq->waker_bfqq;
4924 else if (blocked_bfqq &&
4925 bfq_bfqq_busy(blocked_bfqq) &&
4926 blocked_bfqq->next_rq &&
4927 bfq_serv_to_charge(blocked_bfqq->next_rq,
4928 blocked_bfqq) <=
4929 bfq_bfqq_budget_left(blocked_bfqq)
4930 )
4931 bfqq = blocked_bfqq;
4932 else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
4933 (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
4934 !bfq_bfqq_has_short_ttime(bfqq)))
4935 bfqq = bfq_choose_bfqq_for_injection(bfqd);
4936 else
4937 bfqq = NULL;
4938
4939 goto keep_queue;
4940 }
4941
4942 reason = BFQQE_NO_MORE_REQUESTS;
4943 expire:
4944 bfq_bfqq_expire(bfqd, bfqq, false, reason);
4945 new_queue:
4946 bfqq = bfq_set_in_service_queue(bfqd);
4947 if (bfqq) {
4948 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
4949 goto check_queue;
4950 }
4951 keep_queue:
4952 if (bfqq)
4953 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
4954 else
4955 bfq_log(bfqd, "select_queue: no queue returned");
4956
4957 return bfqq;
4958 }
4959
bfq_update_wr_data(struct bfq_data * bfqd,struct bfq_queue * bfqq)4960 static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4961 {
4962 struct bfq_entity *entity = &bfqq->entity;
4963
4964 if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
4965 bfq_log_bfqq(bfqd, bfqq,
4966 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
4967 jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
4968 jiffies_to_msecs(bfqq->wr_cur_max_time),
4969 bfqq->wr_coeff,
4970 bfqq->entity.weight, bfqq->entity.orig_weight);
4971
4972 if (entity->prio_changed)
4973 bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
4974
4975 /*
4976 * If the queue was activated in a burst, or too much
4977 * time has elapsed from the beginning of this
4978 * weight-raising period, then end weight raising.
4979 */
4980 if (bfq_bfqq_in_large_burst(bfqq))
4981 bfq_bfqq_end_wr(bfqq);
4982 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
4983 bfqq->wr_cur_max_time)) {
4984 if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
4985 time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
4986 bfq_wr_duration(bfqd))) {
4987 /*
4988 * Either in interactive weight
4989 * raising, or in soft_rt weight
4990 * raising with the
4991 * interactive-weight-raising period
4992 * elapsed (so no switch back to
4993 * interactive weight raising).
4994 */
4995 bfq_bfqq_end_wr(bfqq);
4996 } else { /*
4997 * soft_rt finishing while still in
4998 * interactive period, switch back to
4999 * interactive weight raising
5000 */
5001 switch_back_to_interactive_wr(bfqq, bfqd);
5002 bfqq->entity.prio_changed = 1;
5003 }
5004 }
5005 if (bfqq->wr_coeff > 1 &&
5006 bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
5007 bfqq->service_from_wr > max_service_from_wr) {
5008 /* see comments on max_service_from_wr */
5009 bfq_bfqq_end_wr(bfqq);
5010 }
5011 }
5012 /*
5013 * To improve latency (for this or other queues), immediately
5014 * update weight both if it must be raised and if it must be
5015 * lowered. Since, entity may be on some active tree here, and
5016 * might have a pending change of its ioprio class, invoke
5017 * next function with the last parameter unset (see the
5018 * comments on the function).
5019 */
5020 if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
5021 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
5022 entity, false);
5023 }
5024
5025 /*
5026 * Dispatch next request from bfqq.
5027 */
bfq_dispatch_rq_from_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq)5028 static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
5029 struct bfq_queue *bfqq)
5030 {
5031 struct request *rq = bfqq->next_rq;
5032 unsigned long service_to_charge;
5033
5034 service_to_charge = bfq_serv_to_charge(rq, bfqq);
5035
5036 bfq_bfqq_served(bfqq, service_to_charge);
5037
5038 if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
5039 bfqd->wait_dispatch = false;
5040 bfqd->waited_rq = rq;
5041 }
5042
5043 bfq_dispatch_remove(bfqd->queue, rq);
5044
5045 if (bfqq != bfqd->in_service_queue)
5046 goto return_rq;
5047
5048 /*
5049 * If weight raising has to terminate for bfqq, then next
5050 * function causes an immediate update of bfqq's weight,
5051 * without waiting for next activation. As a consequence, on
5052 * expiration, bfqq will be timestamped as if has never been
5053 * weight-raised during this service slot, even if it has
5054 * received part or even most of the service as a
5055 * weight-raised queue. This inflates bfqq's timestamps, which
5056 * is beneficial, as bfqq is then more willing to leave the
5057 * device immediately to possible other weight-raised queues.
5058 */
5059 bfq_update_wr_data(bfqd, bfqq);
5060
5061 /*
5062 * Expire bfqq, pretending that its budget expired, if bfqq
5063 * belongs to CLASS_IDLE and other queues are waiting for
5064 * service.
5065 */
5066 if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
5067 goto return_rq;
5068
5069 bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
5070
5071 return_rq:
5072 return rq;
5073 }
5074
bfq_has_work(struct blk_mq_hw_ctx * hctx)5075 static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
5076 {
5077 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5078
5079 /*
5080 * Avoiding lock: a race on bfqd->queued should cause at
5081 * most a call to dispatch for nothing
5082 */
5083 return !list_empty_careful(&bfqd->dispatch) ||
5084 READ_ONCE(bfqd->queued);
5085 }
5086
__bfq_dispatch_request(struct blk_mq_hw_ctx * hctx)5087 static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5088 {
5089 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5090 struct request *rq = NULL;
5091 struct bfq_queue *bfqq = NULL;
5092
5093 if (!list_empty(&bfqd->dispatch)) {
5094 rq = list_first_entry(&bfqd->dispatch, struct request,
5095 queuelist);
5096 list_del_init(&rq->queuelist);
5097
5098 bfqq = RQ_BFQQ(rq);
5099
5100 if (bfqq) {
5101 /*
5102 * Increment counters here, because this
5103 * dispatch does not follow the standard
5104 * dispatch flow (where counters are
5105 * incremented)
5106 */
5107 bfqq->dispatched++;
5108
5109 goto inc_in_driver_start_rq;
5110 }
5111
5112 /*
5113 * We exploit the bfq_finish_requeue_request hook to
5114 * decrement rq_in_driver, but
5115 * bfq_finish_requeue_request will not be invoked on
5116 * this request. So, to avoid unbalance, just start
5117 * this request, without incrementing rq_in_driver. As
5118 * a negative consequence, rq_in_driver is deceptively
5119 * lower than it should be while this request is in
5120 * service. This may cause bfq_schedule_dispatch to be
5121 * invoked uselessly.
5122 *
5123 * As for implementing an exact solution, the
5124 * bfq_finish_requeue_request hook, if defined, is
5125 * probably invoked also on this request. So, by
5126 * exploiting this hook, we could 1) increment
5127 * rq_in_driver here, and 2) decrement it in
5128 * bfq_finish_requeue_request. Such a solution would
5129 * let the value of the counter be always accurate,
5130 * but it would entail using an extra interface
5131 * function. This cost seems higher than the benefit,
5132 * being the frequency of non-elevator-private
5133 * requests very low.
5134 */
5135 goto start_rq;
5136 }
5137
5138 bfq_log(bfqd, "dispatch requests: %d busy queues",
5139 bfq_tot_busy_queues(bfqd));
5140
5141 if (bfq_tot_busy_queues(bfqd) == 0)
5142 goto exit;
5143
5144 /*
5145 * Force device to serve one request at a time if
5146 * strict_guarantees is true. Forcing this service scheme is
5147 * currently the ONLY way to guarantee that the request
5148 * service order enforced by the scheduler is respected by a
5149 * queueing device. Otherwise the device is free even to make
5150 * some unlucky request wait for as long as the device
5151 * wishes.
5152 *
5153 * Of course, serving one request at a time may cause loss of
5154 * throughput.
5155 */
5156 if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
5157 goto exit;
5158
5159 bfqq = bfq_select_queue(bfqd);
5160 if (!bfqq)
5161 goto exit;
5162
5163 rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
5164
5165 if (rq) {
5166 inc_in_driver_start_rq:
5167 bfqd->rq_in_driver++;
5168 start_rq:
5169 rq->rq_flags |= RQF_STARTED;
5170 }
5171 exit:
5172 return rq;
5173 }
5174
5175 #ifdef CONFIG_BFQ_CGROUP_DEBUG
bfq_update_dispatch_stats(struct request_queue * q,struct request * rq,struct bfq_queue * in_serv_queue,bool idle_timer_disabled)5176 static void bfq_update_dispatch_stats(struct request_queue *q,
5177 struct request *rq,
5178 struct bfq_queue *in_serv_queue,
5179 bool idle_timer_disabled)
5180 {
5181 struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
5182
5183 if (!idle_timer_disabled && !bfqq)
5184 return;
5185
5186 /*
5187 * rq and bfqq are guaranteed to exist until this function
5188 * ends, for the following reasons. First, rq can be
5189 * dispatched to the device, and then can be completed and
5190 * freed, only after this function ends. Second, rq cannot be
5191 * merged (and thus freed because of a merge) any longer,
5192 * because it has already started. Thus rq cannot be freed
5193 * before this function ends, and, since rq has a reference to
5194 * bfqq, the same guarantee holds for bfqq too.
5195 *
5196 * In addition, the following queue lock guarantees that
5197 * bfqq_group(bfqq) exists as well.
5198 */
5199 spin_lock_irq(&q->queue_lock);
5200 if (idle_timer_disabled)
5201 /*
5202 * Since the idle timer has been disabled,
5203 * in_serv_queue contained some request when
5204 * __bfq_dispatch_request was invoked above, which
5205 * implies that rq was picked exactly from
5206 * in_serv_queue. Thus in_serv_queue == bfqq, and is
5207 * therefore guaranteed to exist because of the above
5208 * arguments.
5209 */
5210 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
5211 if (bfqq) {
5212 struct bfq_group *bfqg = bfqq_group(bfqq);
5213
5214 bfqg_stats_update_avg_queue_size(bfqg);
5215 bfqg_stats_set_start_empty_time(bfqg);
5216 bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
5217 }
5218 spin_unlock_irq(&q->queue_lock);
5219 }
5220 #else
bfq_update_dispatch_stats(struct request_queue * q,struct request * rq,struct bfq_queue * in_serv_queue,bool idle_timer_disabled)5221 static inline void bfq_update_dispatch_stats(struct request_queue *q,
5222 struct request *rq,
5223 struct bfq_queue *in_serv_queue,
5224 bool idle_timer_disabled) {}
5225 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
5226
bfq_dispatch_request(struct blk_mq_hw_ctx * hctx)5227 static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5228 {
5229 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5230 struct request *rq;
5231 struct bfq_queue *in_serv_queue;
5232 bool waiting_rq, idle_timer_disabled = false;
5233
5234 spin_lock_irq(&bfqd->lock);
5235
5236 in_serv_queue = bfqd->in_service_queue;
5237 waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
5238
5239 rq = __bfq_dispatch_request(hctx);
5240 if (in_serv_queue == bfqd->in_service_queue) {
5241 idle_timer_disabled =
5242 waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
5243 }
5244
5245 spin_unlock_irq(&bfqd->lock);
5246 bfq_update_dispatch_stats(hctx->queue, rq,
5247 idle_timer_disabled ? in_serv_queue : NULL,
5248 idle_timer_disabled);
5249
5250 return rq;
5251 }
5252
5253 /*
5254 * Task holds one reference to the queue, dropped when task exits. Each rq
5255 * in-flight on this queue also holds a reference, dropped when rq is freed.
5256 *
5257 * Scheduler lock must be held here. Recall not to use bfqq after calling
5258 * this function on it.
5259 */
bfq_put_queue(struct bfq_queue * bfqq)5260 void bfq_put_queue(struct bfq_queue *bfqq)
5261 {
5262 struct bfq_queue *item;
5263 struct hlist_node *n;
5264 struct bfq_group *bfqg = bfqq_group(bfqq);
5265
5266 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref);
5267
5268 bfqq->ref--;
5269 if (bfqq->ref)
5270 return;
5271
5272 if (!hlist_unhashed(&bfqq->burst_list_node)) {
5273 hlist_del_init(&bfqq->burst_list_node);
5274 /*
5275 * Decrement also burst size after the removal, if the
5276 * process associated with bfqq is exiting, and thus
5277 * does not contribute to the burst any longer. This
5278 * decrement helps filter out false positives of large
5279 * bursts, when some short-lived process (often due to
5280 * the execution of commands by some service) happens
5281 * to start and exit while a complex application is
5282 * starting, and thus spawning several processes that
5283 * do I/O (and that *must not* be treated as a large
5284 * burst, see comments on bfq_handle_burst).
5285 *
5286 * In particular, the decrement is performed only if:
5287 * 1) bfqq is not a merged queue, because, if it is,
5288 * then this free of bfqq is not triggered by the exit
5289 * of the process bfqq is associated with, but exactly
5290 * by the fact that bfqq has just been merged.
5291 * 2) burst_size is greater than 0, to handle
5292 * unbalanced decrements. Unbalanced decrements may
5293 * happen in te following case: bfqq is inserted into
5294 * the current burst list--without incrementing
5295 * bust_size--because of a split, but the current
5296 * burst list is not the burst list bfqq belonged to
5297 * (see comments on the case of a split in
5298 * bfq_set_request).
5299 */
5300 if (bfqq->bic && bfqq->bfqd->burst_size > 0)
5301 bfqq->bfqd->burst_size--;
5302 }
5303
5304 /*
5305 * bfqq does not exist any longer, so it cannot be woken by
5306 * any other queue, and cannot wake any other queue. Then bfqq
5307 * must be removed from the woken list of its possible waker
5308 * queue, and all queues in the woken list of bfqq must stop
5309 * having a waker queue. Strictly speaking, these updates
5310 * should be performed when bfqq remains with no I/O source
5311 * attached to it, which happens before bfqq gets freed. In
5312 * particular, this happens when the last process associated
5313 * with bfqq exits or gets associated with a different
5314 * queue. However, both events lead to bfqq being freed soon,
5315 * and dangling references would come out only after bfqq gets
5316 * freed. So these updates are done here, as a simple and safe
5317 * way to handle all cases.
5318 */
5319 /* remove bfqq from woken list */
5320 if (!hlist_unhashed(&bfqq->woken_list_node))
5321 hlist_del_init(&bfqq->woken_list_node);
5322
5323 /* reset waker for all queues in woken list */
5324 hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
5325 woken_list_node) {
5326 item->waker_bfqq = NULL;
5327 hlist_del_init(&item->woken_list_node);
5328 }
5329
5330 if (bfqq->bfqd->last_completed_rq_bfqq == bfqq)
5331 bfqq->bfqd->last_completed_rq_bfqq = NULL;
5332
5333 kmem_cache_free(bfq_pool, bfqq);
5334 bfqg_and_blkg_put(bfqg);
5335 }
5336
bfq_put_stable_ref(struct bfq_queue * bfqq)5337 static void bfq_put_stable_ref(struct bfq_queue *bfqq)
5338 {
5339 bfqq->stable_ref--;
5340 bfq_put_queue(bfqq);
5341 }
5342
bfq_put_cooperator(struct bfq_queue * bfqq)5343 void bfq_put_cooperator(struct bfq_queue *bfqq)
5344 {
5345 struct bfq_queue *__bfqq, *next;
5346
5347 /*
5348 * If this queue was scheduled to merge with another queue, be
5349 * sure to drop the reference taken on that queue (and others in
5350 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
5351 */
5352 __bfqq = bfqq->new_bfqq;
5353 while (__bfqq) {
5354 if (__bfqq == bfqq)
5355 break;
5356 next = __bfqq->new_bfqq;
5357 bfq_put_queue(__bfqq);
5358 __bfqq = next;
5359 }
5360 }
5361
bfq_exit_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq)5362 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
5363 {
5364 if (bfqq == bfqd->in_service_queue) {
5365 __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
5366 bfq_schedule_dispatch(bfqd);
5367 }
5368
5369 bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
5370
5371 bfq_put_cooperator(bfqq);
5372
5373 bfq_release_process_ref(bfqd, bfqq);
5374 }
5375
bfq_exit_icq_bfqq(struct bfq_io_cq * bic,bool is_sync)5376 static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
5377 {
5378 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
5379 struct bfq_data *bfqd;
5380
5381 if (bfqq)
5382 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
5383
5384 if (bfqq && bfqd) {
5385 unsigned long flags;
5386
5387 spin_lock_irqsave(&bfqd->lock, flags);
5388 bic_set_bfqq(bic, NULL, is_sync);
5389 bfq_exit_bfqq(bfqd, bfqq);
5390 spin_unlock_irqrestore(&bfqd->lock, flags);
5391 }
5392 }
5393
bfq_exit_icq(struct io_cq * icq)5394 static void bfq_exit_icq(struct io_cq *icq)
5395 {
5396 struct bfq_io_cq *bic = icq_to_bic(icq);
5397
5398 if (bic->stable_merge_bfqq) {
5399 struct bfq_data *bfqd = bic->stable_merge_bfqq->bfqd;
5400
5401 /*
5402 * bfqd is NULL if scheduler already exited, and in
5403 * that case this is the last time bfqq is accessed.
5404 */
5405 if (bfqd) {
5406 unsigned long flags;
5407
5408 spin_lock_irqsave(&bfqd->lock, flags);
5409 bfq_put_stable_ref(bic->stable_merge_bfqq);
5410 spin_unlock_irqrestore(&bfqd->lock, flags);
5411 } else {
5412 bfq_put_stable_ref(bic->stable_merge_bfqq);
5413 }
5414 }
5415
5416 bfq_exit_icq_bfqq(bic, true);
5417 bfq_exit_icq_bfqq(bic, false);
5418 }
5419
5420 /*
5421 * Update the entity prio values; note that the new values will not
5422 * be used until the next (re)activation.
5423 */
5424 static void
bfq_set_next_ioprio_data(struct bfq_queue * bfqq,struct bfq_io_cq * bic)5425 bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
5426 {
5427 struct task_struct *tsk = current;
5428 int ioprio_class;
5429 struct bfq_data *bfqd = bfqq->bfqd;
5430
5431 if (!bfqd)
5432 return;
5433
5434 ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5435 switch (ioprio_class) {
5436 default:
5437 pr_err("bdi %s: bfq: bad prio class %d\n",
5438 bdi_dev_name(bfqq->bfqd->queue->disk->bdi),
5439 ioprio_class);
5440 fallthrough;
5441 case IOPRIO_CLASS_NONE:
5442 /*
5443 * No prio set, inherit CPU scheduling settings.
5444 */
5445 bfqq->new_ioprio = task_nice_ioprio(tsk);
5446 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
5447 break;
5448 case IOPRIO_CLASS_RT:
5449 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5450 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
5451 break;
5452 case IOPRIO_CLASS_BE:
5453 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5454 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
5455 break;
5456 case IOPRIO_CLASS_IDLE:
5457 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5458 bfqq->new_ioprio = 7;
5459 break;
5460 }
5461
5462 if (bfqq->new_ioprio >= IOPRIO_NR_LEVELS) {
5463 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5464 bfqq->new_ioprio);
5465 bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
5466 }
5467
5468 bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
5469 bfq_log_bfqq(bfqd, bfqq, "new_ioprio %d new_weight %d",
5470 bfqq->new_ioprio, bfqq->entity.new_weight);
5471 bfqq->entity.prio_changed = 1;
5472 }
5473
5474 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5475 struct bio *bio, bool is_sync,
5476 struct bfq_io_cq *bic,
5477 bool respawn);
5478
bfq_check_ioprio_change(struct bfq_io_cq * bic,struct bio * bio)5479 static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5480 {
5481 struct bfq_data *bfqd = bic_to_bfqd(bic);
5482 struct bfq_queue *bfqq;
5483 int ioprio = bic->icq.ioc->ioprio;
5484
5485 /*
5486 * This condition may trigger on a newly created bic, be sure to
5487 * drop the lock before returning.
5488 */
5489 if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5490 return;
5491
5492 bic->ioprio = ioprio;
5493
5494 bfqq = bic_to_bfqq(bic, false);
5495 if (bfqq) {
5496 struct bfq_queue *old_bfqq = bfqq;
5497
5498 bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
5499 bic_set_bfqq(bic, bfqq, false);
5500 bfq_release_process_ref(bfqd, old_bfqq);
5501 }
5502
5503 bfqq = bic_to_bfqq(bic, true);
5504 if (bfqq)
5505 bfq_set_next_ioprio_data(bfqq, bic);
5506 }
5507
bfq_init_bfqq(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct bfq_io_cq * bic,pid_t pid,int is_sync)5508 static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5509 struct bfq_io_cq *bic, pid_t pid, int is_sync)
5510 {
5511 u64 now_ns = ktime_get_ns();
5512
5513 RB_CLEAR_NODE(&bfqq->entity.rb_node);
5514 INIT_LIST_HEAD(&bfqq->fifo);
5515 INIT_HLIST_NODE(&bfqq->burst_list_node);
5516 INIT_HLIST_NODE(&bfqq->woken_list_node);
5517 INIT_HLIST_HEAD(&bfqq->woken_list);
5518
5519 bfqq->ref = 0;
5520 bfqq->bfqd = bfqd;
5521
5522 if (bic)
5523 bfq_set_next_ioprio_data(bfqq, bic);
5524
5525 if (is_sync) {
5526 /*
5527 * No need to mark as has_short_ttime if in
5528 * idle_class, because no device idling is performed
5529 * for queues in idle class
5530 */
5531 if (!bfq_class_idle(bfqq))
5532 /* tentatively mark as has_short_ttime */
5533 bfq_mark_bfqq_has_short_ttime(bfqq);
5534 bfq_mark_bfqq_sync(bfqq);
5535 bfq_mark_bfqq_just_created(bfqq);
5536 } else
5537 bfq_clear_bfqq_sync(bfqq);
5538
5539 /* set end request to minus infinity from now */
5540 bfqq->ttime.last_end_request = now_ns + 1;
5541
5542 bfqq->creation_time = jiffies;
5543
5544 bfqq->io_start_time = now_ns;
5545
5546 bfq_mark_bfqq_IO_bound(bfqq);
5547
5548 bfqq->pid = pid;
5549
5550 /* Tentative initial value to trade off between thr and lat */
5551 bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5552 bfqq->budget_timeout = bfq_smallest_from_now();
5553
5554 bfqq->wr_coeff = 1;
5555 bfqq->last_wr_start_finish = jiffies;
5556 bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5557 bfqq->split_time = bfq_smallest_from_now();
5558
5559 /*
5560 * To not forget the possibly high bandwidth consumed by a
5561 * process/queue in the recent past,
5562 * bfq_bfqq_softrt_next_start() returns a value at least equal
5563 * to the current value of bfqq->soft_rt_next_start (see
5564 * comments on bfq_bfqq_softrt_next_start). Set
5565 * soft_rt_next_start to now, to mean that bfqq has consumed
5566 * no bandwidth so far.
5567 */
5568 bfqq->soft_rt_next_start = jiffies;
5569
5570 /* first request is almost certainly seeky */
5571 bfqq->seek_history = 1;
5572 }
5573
bfq_async_queue_prio(struct bfq_data * bfqd,struct bfq_group * bfqg,int ioprio_class,int ioprio)5574 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5575 struct bfq_group *bfqg,
5576 int ioprio_class, int ioprio)
5577 {
5578 switch (ioprio_class) {
5579 case IOPRIO_CLASS_RT:
5580 return &bfqg->async_bfqq[0][ioprio];
5581 case IOPRIO_CLASS_NONE:
5582 ioprio = IOPRIO_BE_NORM;
5583 fallthrough;
5584 case IOPRIO_CLASS_BE:
5585 return &bfqg->async_bfqq[1][ioprio];
5586 case IOPRIO_CLASS_IDLE:
5587 return &bfqg->async_idle_bfqq;
5588 default:
5589 return NULL;
5590 }
5591 }
5592
5593 static struct bfq_queue *
bfq_do_early_stable_merge(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct bfq_io_cq * bic,struct bfq_queue * last_bfqq_created)5594 bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5595 struct bfq_io_cq *bic,
5596 struct bfq_queue *last_bfqq_created)
5597 {
5598 struct bfq_queue *new_bfqq =
5599 bfq_setup_merge(bfqq, last_bfqq_created);
5600
5601 if (!new_bfqq)
5602 return bfqq;
5603
5604 if (new_bfqq->bic)
5605 new_bfqq->bic->stably_merged = true;
5606 bic->stably_merged = true;
5607
5608 /*
5609 * Reusing merge functions. This implies that
5610 * bfqq->bic must be set too, for
5611 * bfq_merge_bfqqs to correctly save bfqq's
5612 * state before killing it.
5613 */
5614 bfqq->bic = bic;
5615 bfq_merge_bfqqs(bfqd, bic, bfqq, new_bfqq);
5616
5617 return new_bfqq;
5618 }
5619
5620 /*
5621 * Many throughput-sensitive workloads are made of several parallel
5622 * I/O flows, with all flows generated by the same application, or
5623 * more generically by the same task (e.g., system boot). The most
5624 * counterproductive action with these workloads is plugging I/O
5625 * dispatch when one of the bfq_queues associated with these flows
5626 * remains temporarily empty.
5627 *
5628 * To avoid this plugging, BFQ has been using a burst-handling
5629 * mechanism for years now. This mechanism has proven effective for
5630 * throughput, and not detrimental for service guarantees. The
5631 * following function pushes this mechanism a little bit further,
5632 * basing on the following two facts.
5633 *
5634 * First, all the I/O flows of a the same application or task
5635 * contribute to the execution/completion of that common application
5636 * or task. So the performance figures that matter are total
5637 * throughput of the flows and task-wide I/O latency. In particular,
5638 * these flows do not need to be protected from each other, in terms
5639 * of individual bandwidth or latency.
5640 *
5641 * Second, the above fact holds regardless of the number of flows.
5642 *
5643 * Putting these two facts together, this commits merges stably the
5644 * bfq_queues associated with these I/O flows, i.e., with the
5645 * processes that generate these IO/ flows, regardless of how many the
5646 * involved processes are.
5647 *
5648 * To decide whether a set of bfq_queues is actually associated with
5649 * the I/O flows of a common application or task, and to merge these
5650 * queues stably, this function operates as follows: given a bfq_queue,
5651 * say Q2, currently being created, and the last bfq_queue, say Q1,
5652 * created before Q2, Q2 is merged stably with Q1 if
5653 * - very little time has elapsed since when Q1 was created
5654 * - Q2 has the same ioprio as Q1
5655 * - Q2 belongs to the same group as Q1
5656 *
5657 * Merging bfq_queues also reduces scheduling overhead. A fio test
5658 * with ten random readers on /dev/nullb shows a throughput boost of
5659 * 40%, with a quadcore. Since BFQ's execution time amounts to ~50% of
5660 * the total per-request processing time, the above throughput boost
5661 * implies that BFQ's overhead is reduced by more than 50%.
5662 *
5663 * This new mechanism most certainly obsoletes the current
5664 * burst-handling heuristics. We keep those heuristics for the moment.
5665 */
bfq_do_or_sched_stable_merge(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct bfq_io_cq * bic)5666 static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
5667 struct bfq_queue *bfqq,
5668 struct bfq_io_cq *bic)
5669 {
5670 struct bfq_queue **source_bfqq = bfqq->entity.parent ?
5671 &bfqq->entity.parent->last_bfqq_created :
5672 &bfqd->last_bfqq_created;
5673
5674 struct bfq_queue *last_bfqq_created = *source_bfqq;
5675
5676 /*
5677 * If last_bfqq_created has not been set yet, then init it. If
5678 * it has been set already, but too long ago, then move it
5679 * forward to bfqq. Finally, move also if bfqq belongs to a
5680 * different group than last_bfqq_created, or if bfqq has a
5681 * different ioprio or ioprio_class. If none of these
5682 * conditions holds true, then try an early stable merge or
5683 * schedule a delayed stable merge.
5684 *
5685 * A delayed merge is scheduled (instead of performing an
5686 * early merge), in case bfqq might soon prove to be more
5687 * throughput-beneficial if not merged. Currently this is
5688 * possible only if bfqd is rotational with no queueing. For
5689 * such a drive, not merging bfqq is better for throughput if
5690 * bfqq happens to contain sequential I/O. So, we wait a
5691 * little bit for enough I/O to flow through bfqq. After that,
5692 * if such an I/O is sequential, then the merge is
5693 * canceled. Otherwise the merge is finally performed.
5694 */
5695 if (!last_bfqq_created ||
5696 time_before(last_bfqq_created->creation_time +
5697 msecs_to_jiffies(bfq_activation_stable_merging),
5698 bfqq->creation_time) ||
5699 bfqq->entity.parent != last_bfqq_created->entity.parent ||
5700 bfqq->ioprio != last_bfqq_created->ioprio ||
5701 bfqq->ioprio_class != last_bfqq_created->ioprio_class)
5702 *source_bfqq = bfqq;
5703 else if (time_after_eq(last_bfqq_created->creation_time +
5704 bfqd->bfq_burst_interval,
5705 bfqq->creation_time)) {
5706 if (likely(bfqd->nonrot_with_queueing))
5707 /*
5708 * With this type of drive, leaving
5709 * bfqq alone may provide no
5710 * throughput benefits compared with
5711 * merging bfqq. So merge bfqq now.
5712 */
5713 bfqq = bfq_do_early_stable_merge(bfqd, bfqq,
5714 bic,
5715 last_bfqq_created);
5716 else { /* schedule tentative stable merge */
5717 /*
5718 * get reference on last_bfqq_created,
5719 * to prevent it from being freed,
5720 * until we decide whether to merge
5721 */
5722 last_bfqq_created->ref++;
5723 /*
5724 * need to keep track of stable refs, to
5725 * compute process refs correctly
5726 */
5727 last_bfqq_created->stable_ref++;
5728 /*
5729 * Record the bfqq to merge to.
5730 */
5731 bic->stable_merge_bfqq = last_bfqq_created;
5732 }
5733 }
5734
5735 return bfqq;
5736 }
5737
5738
bfq_get_queue(struct bfq_data * bfqd,struct bio * bio,bool is_sync,struct bfq_io_cq * bic,bool respawn)5739 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5740 struct bio *bio, bool is_sync,
5741 struct bfq_io_cq *bic,
5742 bool respawn)
5743 {
5744 const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5745 const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5746 struct bfq_queue **async_bfqq = NULL;
5747 struct bfq_queue *bfqq;
5748 struct bfq_group *bfqg;
5749
5750 bfqg = bfq_bio_bfqg(bfqd, bio);
5751 if (!is_sync) {
5752 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5753 ioprio);
5754 bfqq = *async_bfqq;
5755 if (bfqq)
5756 goto out;
5757 }
5758
5759 bfqq = kmem_cache_alloc_node(bfq_pool,
5760 GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5761 bfqd->queue->node);
5762
5763 if (bfqq) {
5764 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5765 is_sync);
5766 bfq_init_entity(&bfqq->entity, bfqg);
5767 bfq_log_bfqq(bfqd, bfqq, "allocated");
5768 } else {
5769 bfqq = &bfqd->oom_bfqq;
5770 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5771 goto out;
5772 }
5773
5774 /*
5775 * Pin the queue now that it's allocated, scheduler exit will
5776 * prune it.
5777 */
5778 if (async_bfqq) {
5779 bfqq->ref++; /*
5780 * Extra group reference, w.r.t. sync
5781 * queue. This extra reference is removed
5782 * only if bfqq->bfqg disappears, to
5783 * guarantee that this queue is not freed
5784 * until its group goes away.
5785 */
5786 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5787 bfqq, bfqq->ref);
5788 *async_bfqq = bfqq;
5789 }
5790
5791 out:
5792 bfqq->ref++; /* get a process reference to this queue */
5793
5794 if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn)
5795 bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic);
5796 return bfqq;
5797 }
5798
bfq_update_io_thinktime(struct bfq_data * bfqd,struct bfq_queue * bfqq)5799 static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5800 struct bfq_queue *bfqq)
5801 {
5802 struct bfq_ttime *ttime = &bfqq->ttime;
5803 u64 elapsed;
5804
5805 /*
5806 * We are really interested in how long it takes for the queue to
5807 * become busy when there is no outstanding IO for this queue. So
5808 * ignore cases when the bfq queue has already IO queued.
5809 */
5810 if (bfqq->dispatched || bfq_bfqq_busy(bfqq))
5811 return;
5812 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
5813 elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5814
5815 ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
5816 ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
5817 ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5818 ttime->ttime_samples);
5819 }
5820
5821 static void
bfq_update_io_seektime(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct request * rq)5822 bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5823 struct request *rq)
5824 {
5825 bfqq->seek_history <<= 1;
5826 bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5827
5828 if (bfqq->wr_coeff > 1 &&
5829 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5830 BFQQ_TOTALLY_SEEKY(bfqq)) {
5831 if (time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
5832 bfq_wr_duration(bfqd))) {
5833 /*
5834 * In soft_rt weight raising with the
5835 * interactive-weight-raising period
5836 * elapsed (so no switch back to
5837 * interactive weight raising).
5838 */
5839 bfq_bfqq_end_wr(bfqq);
5840 } else { /*
5841 * stopping soft_rt weight raising
5842 * while still in interactive period,
5843 * switch back to interactive weight
5844 * raising
5845 */
5846 switch_back_to_interactive_wr(bfqq, bfqd);
5847 bfqq->entity.prio_changed = 1;
5848 }
5849 }
5850 }
5851
bfq_update_has_short_ttime(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct bfq_io_cq * bic)5852 static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5853 struct bfq_queue *bfqq,
5854 struct bfq_io_cq *bic)
5855 {
5856 bool has_short_ttime = true, state_changed;
5857
5858 /*
5859 * No need to update has_short_ttime if bfqq is async or in
5860 * idle io prio class, or if bfq_slice_idle is zero, because
5861 * no device idling is performed for bfqq in this case.
5862 */
5863 if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5864 bfqd->bfq_slice_idle == 0)
5865 return;
5866
5867 /* Idle window just restored, statistics are meaningless. */
5868 if (time_is_after_eq_jiffies(bfqq->split_time +
5869 bfqd->bfq_wr_min_idle_time))
5870 return;
5871
5872 /* Think time is infinite if no process is linked to
5873 * bfqq. Otherwise check average think time to decide whether
5874 * to mark as has_short_ttime. To this goal, compare average
5875 * think time with half the I/O-plugging timeout.
5876 */
5877 if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
5878 (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5879 bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle>>1))
5880 has_short_ttime = false;
5881
5882 state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5883
5884 if (has_short_ttime)
5885 bfq_mark_bfqq_has_short_ttime(bfqq);
5886 else
5887 bfq_clear_bfqq_has_short_ttime(bfqq);
5888
5889 /*
5890 * Until the base value for the total service time gets
5891 * finally computed for bfqq, the inject limit does depend on
5892 * the think-time state (short|long). In particular, the limit
5893 * is 0 or 1 if the think time is deemed, respectively, as
5894 * short or long (details in the comments in
5895 * bfq_update_inject_limit()). Accordingly, the next
5896 * instructions reset the inject limit if the think-time state
5897 * has changed and the above base value is still to be
5898 * computed.
5899 *
5900 * However, the reset is performed only if more than 100 ms
5901 * have elapsed since the last update of the inject limit, or
5902 * (inclusive) if the change is from short to long think
5903 * time. The reason for this waiting is as follows.
5904 *
5905 * bfqq may have a long think time because of a
5906 * synchronization with some other queue, i.e., because the
5907 * I/O of some other queue may need to be completed for bfqq
5908 * to receive new I/O. Details in the comments on the choice
5909 * of the queue for injection in bfq_select_queue().
5910 *
5911 * As stressed in those comments, if such a synchronization is
5912 * actually in place, then, without injection on bfqq, the
5913 * blocking I/O cannot happen to served while bfqq is in
5914 * service. As a consequence, if bfqq is granted
5915 * I/O-dispatch-plugging, then bfqq remains empty, and no I/O
5916 * is dispatched, until the idle timeout fires. This is likely
5917 * to result in lower bandwidth and higher latencies for bfqq,
5918 * and in a severe loss of total throughput.
5919 *
5920 * On the opposite end, a non-zero inject limit may allow the
5921 * I/O that blocks bfqq to be executed soon, and therefore
5922 * bfqq to receive new I/O soon.
5923 *
5924 * But, if the blocking gets actually eliminated, then the
5925 * next think-time sample for bfqq may be very low. This in
5926 * turn may cause bfqq's think time to be deemed
5927 * short. Without the 100 ms barrier, this new state change
5928 * would cause the body of the next if to be executed
5929 * immediately. But this would set to 0 the inject
5930 * limit. Without injection, the blocking I/O would cause the
5931 * think time of bfqq to become long again, and therefore the
5932 * inject limit to be raised again, and so on. The only effect
5933 * of such a steady oscillation between the two think-time
5934 * states would be to prevent effective injection on bfqq.
5935 *
5936 * In contrast, if the inject limit is not reset during such a
5937 * long time interval as 100 ms, then the number of short
5938 * think time samples can grow significantly before the reset
5939 * is performed. As a consequence, the think time state can
5940 * become stable before the reset. Therefore there will be no
5941 * state change when the 100 ms elapse, and no reset of the
5942 * inject limit. The inject limit remains steadily equal to 1
5943 * both during and after the 100 ms. So injection can be
5944 * performed at all times, and throughput gets boosted.
5945 *
5946 * An inject limit equal to 1 is however in conflict, in
5947 * general, with the fact that the think time of bfqq is
5948 * short, because injection may be likely to delay bfqq's I/O
5949 * (as explained in the comments in
5950 * bfq_update_inject_limit()). But this does not happen in
5951 * this special case, because bfqq's low think time is due to
5952 * an effective handling of a synchronization, through
5953 * injection. In this special case, bfqq's I/O does not get
5954 * delayed by injection; on the contrary, bfqq's I/O is
5955 * brought forward, because it is not blocked for
5956 * milliseconds.
5957 *
5958 * In addition, serving the blocking I/O much sooner, and much
5959 * more frequently than once per I/O-plugging timeout, makes
5960 * it much quicker to detect a waker queue (the concept of
5961 * waker queue is defined in the comments in
5962 * bfq_add_request()). This makes it possible to start sooner
5963 * to boost throughput more effectively, by injecting the I/O
5964 * of the waker queue unconditionally on every
5965 * bfq_dispatch_request().
5966 *
5967 * One last, important benefit of not resetting the inject
5968 * limit before 100 ms is that, during this time interval, the
5969 * base value for the total service time is likely to get
5970 * finally computed for bfqq, freeing the inject limit from
5971 * its relation with the think time.
5972 */
5973 if (state_changed && bfqq->last_serv_time_ns == 0 &&
5974 (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
5975 msecs_to_jiffies(100)) ||
5976 !has_short_ttime))
5977 bfq_reset_inject_limit(bfqd, bfqq);
5978 }
5979
5980 /*
5981 * Called when a new fs request (rq) is added to bfqq. Check if there's
5982 * something we should do about it.
5983 */
bfq_rq_enqueued(struct bfq_data * bfqd,struct bfq_queue * bfqq,struct request * rq)5984 static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5985 struct request *rq)
5986 {
5987 if (rq->cmd_flags & REQ_META)
5988 bfqq->meta_pending++;
5989
5990 bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
5991
5992 if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
5993 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
5994 blk_rq_sectors(rq) < 32;
5995 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
5996
5997 /*
5998 * There is just this request queued: if
5999 * - the request is small, and
6000 * - we are idling to boost throughput, and
6001 * - the queue is not to be expired,
6002 * then just exit.
6003 *
6004 * In this way, if the device is being idled to wait
6005 * for a new request from the in-service queue, we
6006 * avoid unplugging the device and committing the
6007 * device to serve just a small request. In contrast
6008 * we wait for the block layer to decide when to
6009 * unplug the device: hopefully, new requests will be
6010 * merged to this one quickly, then the device will be
6011 * unplugged and larger requests will be dispatched.
6012 */
6013 if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
6014 !budget_timeout)
6015 return;
6016
6017 /*
6018 * A large enough request arrived, or idling is being
6019 * performed to preserve service guarantees, or
6020 * finally the queue is to be expired: in all these
6021 * cases disk idling is to be stopped, so clear
6022 * wait_request flag and reset timer.
6023 */
6024 bfq_clear_bfqq_wait_request(bfqq);
6025 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
6026
6027 /*
6028 * The queue is not empty, because a new request just
6029 * arrived. Hence we can safely expire the queue, in
6030 * case of budget timeout, without risking that the
6031 * timestamps of the queue are not updated correctly.
6032 * See [1] for more details.
6033 */
6034 if (budget_timeout)
6035 bfq_bfqq_expire(bfqd, bfqq, false,
6036 BFQQE_BUDGET_TIMEOUT);
6037 }
6038 }
6039
bfqq_request_allocated(struct bfq_queue * bfqq)6040 static void bfqq_request_allocated(struct bfq_queue *bfqq)
6041 {
6042 struct bfq_entity *entity = &bfqq->entity;
6043
6044 for_each_entity(entity)
6045 entity->allocated++;
6046 }
6047
bfqq_request_freed(struct bfq_queue * bfqq)6048 static void bfqq_request_freed(struct bfq_queue *bfqq)
6049 {
6050 struct bfq_entity *entity = &bfqq->entity;
6051
6052 for_each_entity(entity)
6053 entity->allocated--;
6054 }
6055
6056 /* returns true if it causes the idle timer to be disabled */
__bfq_insert_request(struct bfq_data * bfqd,struct request * rq)6057 static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
6058 {
6059 struct bfq_queue *bfqq = RQ_BFQQ(rq),
6060 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true,
6061 RQ_BIC(rq));
6062 bool waiting, idle_timer_disabled = false;
6063
6064 if (new_bfqq) {
6065 /*
6066 * Release the request's reference to the old bfqq
6067 * and make sure one is taken to the shared queue.
6068 */
6069 bfqq_request_allocated(new_bfqq);
6070 bfqq_request_freed(bfqq);
6071 new_bfqq->ref++;
6072 /*
6073 * If the bic associated with the process
6074 * issuing this request still points to bfqq
6075 * (and thus has not been already redirected
6076 * to new_bfqq or even some other bfq_queue),
6077 * then complete the merge and redirect it to
6078 * new_bfqq.
6079 */
6080 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
6081 bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
6082 bfqq, new_bfqq);
6083
6084 bfq_clear_bfqq_just_created(bfqq);
6085 /*
6086 * rq is about to be enqueued into new_bfqq,
6087 * release rq reference on bfqq
6088 */
6089 bfq_put_queue(bfqq);
6090 rq->elv.priv[1] = new_bfqq;
6091 bfqq = new_bfqq;
6092 }
6093
6094 bfq_update_io_thinktime(bfqd, bfqq);
6095 bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
6096 bfq_update_io_seektime(bfqd, bfqq, rq);
6097
6098 waiting = bfqq && bfq_bfqq_wait_request(bfqq);
6099 bfq_add_request(rq);
6100 idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
6101
6102 rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
6103 list_add_tail(&rq->queuelist, &bfqq->fifo);
6104
6105 bfq_rq_enqueued(bfqd, bfqq, rq);
6106
6107 return idle_timer_disabled;
6108 }
6109
6110 #ifdef CONFIG_BFQ_CGROUP_DEBUG
bfq_update_insert_stats(struct request_queue * q,struct bfq_queue * bfqq,bool idle_timer_disabled,blk_opf_t cmd_flags)6111 static void bfq_update_insert_stats(struct request_queue *q,
6112 struct bfq_queue *bfqq,
6113 bool idle_timer_disabled,
6114 blk_opf_t cmd_flags)
6115 {
6116 if (!bfqq)
6117 return;
6118
6119 /*
6120 * bfqq still exists, because it can disappear only after
6121 * either it is merged with another queue, or the process it
6122 * is associated with exits. But both actions must be taken by
6123 * the same process currently executing this flow of
6124 * instructions.
6125 *
6126 * In addition, the following queue lock guarantees that
6127 * bfqq_group(bfqq) exists as well.
6128 */
6129 spin_lock_irq(&q->queue_lock);
6130 bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
6131 if (idle_timer_disabled)
6132 bfqg_stats_update_idle_time(bfqq_group(bfqq));
6133 spin_unlock_irq(&q->queue_lock);
6134 }
6135 #else
bfq_update_insert_stats(struct request_queue * q,struct bfq_queue * bfqq,bool idle_timer_disabled,blk_opf_t cmd_flags)6136 static inline void bfq_update_insert_stats(struct request_queue *q,
6137 struct bfq_queue *bfqq,
6138 bool idle_timer_disabled,
6139 blk_opf_t cmd_flags) {}
6140 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
6141
6142 static struct bfq_queue *bfq_init_rq(struct request *rq);
6143
bfq_insert_request(struct blk_mq_hw_ctx * hctx,struct request * rq,bool at_head)6144 static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
6145 bool at_head)
6146 {
6147 struct request_queue *q = hctx->queue;
6148 struct bfq_data *bfqd = q->elevator->elevator_data;
6149 struct bfq_queue *bfqq;
6150 bool idle_timer_disabled = false;
6151 blk_opf_t cmd_flags;
6152 LIST_HEAD(free);
6153
6154 #ifdef CONFIG_BFQ_GROUP_IOSCHED
6155 if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
6156 bfqg_stats_update_legacy_io(q, rq);
6157 #endif
6158 spin_lock_irq(&bfqd->lock);
6159 bfqq = bfq_init_rq(rq);
6160 if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
6161 spin_unlock_irq(&bfqd->lock);
6162 blk_mq_free_requests(&free);
6163 return;
6164 }
6165
6166 trace_block_rq_insert(rq);
6167
6168 if (!bfqq || at_head) {
6169 if (at_head)
6170 list_add(&rq->queuelist, &bfqd->dispatch);
6171 else
6172 list_add_tail(&rq->queuelist, &bfqd->dispatch);
6173 } else {
6174 idle_timer_disabled = __bfq_insert_request(bfqd, rq);
6175 /*
6176 * Update bfqq, because, if a queue merge has occurred
6177 * in __bfq_insert_request, then rq has been
6178 * redirected into a new queue.
6179 */
6180 bfqq = RQ_BFQQ(rq);
6181
6182 if (rq_mergeable(rq)) {
6183 elv_rqhash_add(q, rq);
6184 if (!q->last_merge)
6185 q->last_merge = rq;
6186 }
6187 }
6188
6189 /*
6190 * Cache cmd_flags before releasing scheduler lock, because rq
6191 * may disappear afterwards (for example, because of a request
6192 * merge).
6193 */
6194 cmd_flags = rq->cmd_flags;
6195 spin_unlock_irq(&bfqd->lock);
6196
6197 bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
6198 cmd_flags);
6199 }
6200
bfq_insert_requests(struct blk_mq_hw_ctx * hctx,struct list_head * list,bool at_head)6201 static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
6202 struct list_head *list, bool at_head)
6203 {
6204 while (!list_empty(list)) {
6205 struct request *rq;
6206
6207 rq = list_first_entry(list, struct request, queuelist);
6208 list_del_init(&rq->queuelist);
6209 bfq_insert_request(hctx, rq, at_head);
6210 }
6211 }
6212
bfq_update_hw_tag(struct bfq_data * bfqd)6213 static void bfq_update_hw_tag(struct bfq_data *bfqd)
6214 {
6215 struct bfq_queue *bfqq = bfqd->in_service_queue;
6216
6217 bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
6218 bfqd->rq_in_driver);
6219
6220 if (bfqd->hw_tag == 1)
6221 return;
6222
6223 /*
6224 * This sample is valid if the number of outstanding requests
6225 * is large enough to allow a queueing behavior. Note that the
6226 * sum is not exact, as it's not taking into account deactivated
6227 * requests.
6228 */
6229 if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
6230 return;
6231
6232 /*
6233 * If active queue hasn't enough requests and can idle, bfq might not
6234 * dispatch sufficient requests to hardware. Don't zero hw_tag in this
6235 * case
6236 */
6237 if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
6238 bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
6239 BFQ_HW_QUEUE_THRESHOLD &&
6240 bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
6241 return;
6242
6243 if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
6244 return;
6245
6246 bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
6247 bfqd->max_rq_in_driver = 0;
6248 bfqd->hw_tag_samples = 0;
6249
6250 bfqd->nonrot_with_queueing =
6251 blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
6252 }
6253
bfq_completed_request(struct bfq_queue * bfqq,struct bfq_data * bfqd)6254 static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
6255 {
6256 u64 now_ns;
6257 u32 delta_us;
6258
6259 bfq_update_hw_tag(bfqd);
6260
6261 bfqd->rq_in_driver--;
6262 bfqq->dispatched--;
6263
6264 if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
6265 /*
6266 * Set budget_timeout (which we overload to store the
6267 * time at which the queue remains with no backlog and
6268 * no outstanding request; used by the weight-raising
6269 * mechanism).
6270 */
6271 bfqq->budget_timeout = jiffies;
6272
6273 bfq_weights_tree_remove(bfqd, bfqq);
6274 }
6275
6276 now_ns = ktime_get_ns();
6277
6278 bfqq->ttime.last_end_request = now_ns;
6279
6280 /*
6281 * Using us instead of ns, to get a reasonable precision in
6282 * computing rate in next check.
6283 */
6284 delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
6285
6286 /*
6287 * If the request took rather long to complete, and, according
6288 * to the maximum request size recorded, this completion latency
6289 * implies that the request was certainly served at a very low
6290 * rate (less than 1M sectors/sec), then the whole observation
6291 * interval that lasts up to this time instant cannot be a
6292 * valid time interval for computing a new peak rate. Invoke
6293 * bfq_update_rate_reset to have the following three steps
6294 * taken:
6295 * - close the observation interval at the last (previous)
6296 * request dispatch or completion
6297 * - compute rate, if possible, for that observation interval
6298 * - reset to zero samples, which will trigger a proper
6299 * re-initialization of the observation interval on next
6300 * dispatch
6301 */
6302 if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
6303 (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
6304 1UL<<(BFQ_RATE_SHIFT - 10))
6305 bfq_update_rate_reset(bfqd, NULL);
6306 bfqd->last_completion = now_ns;
6307 /*
6308 * Shared queues are likely to receive I/O at a high
6309 * rate. This may deceptively let them be considered as wakers
6310 * of other queues. But a false waker will unjustly steal
6311 * bandwidth to its supposedly woken queue. So considering
6312 * also shared queues in the waking mechanism may cause more
6313 * control troubles than throughput benefits. Then reset
6314 * last_completed_rq_bfqq if bfqq is a shared queue.
6315 */
6316 if (!bfq_bfqq_coop(bfqq))
6317 bfqd->last_completed_rq_bfqq = bfqq;
6318 else
6319 bfqd->last_completed_rq_bfqq = NULL;
6320
6321 /*
6322 * If we are waiting to discover whether the request pattern
6323 * of the task associated with the queue is actually
6324 * isochronous, and both requisites for this condition to hold
6325 * are now satisfied, then compute soft_rt_next_start (see the
6326 * comments on the function bfq_bfqq_softrt_next_start()). We
6327 * do not compute soft_rt_next_start if bfqq is in interactive
6328 * weight raising (see the comments in bfq_bfqq_expire() for
6329 * an explanation). We schedule this delayed update when bfqq
6330 * expires, if it still has in-flight requests.
6331 */
6332 if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
6333 RB_EMPTY_ROOT(&bfqq->sort_list) &&
6334 bfqq->wr_coeff != bfqd->bfq_wr_coeff)
6335 bfqq->soft_rt_next_start =
6336 bfq_bfqq_softrt_next_start(bfqd, bfqq);
6337
6338 /*
6339 * If this is the in-service queue, check if it needs to be expired,
6340 * or if we want to idle in case it has no pending requests.
6341 */
6342 if (bfqd->in_service_queue == bfqq) {
6343 if (bfq_bfqq_must_idle(bfqq)) {
6344 if (bfqq->dispatched == 0)
6345 bfq_arm_slice_timer(bfqd);
6346 /*
6347 * If we get here, we do not expire bfqq, even
6348 * if bfqq was in budget timeout or had no
6349 * more requests (as controlled in the next
6350 * conditional instructions). The reason for
6351 * not expiring bfqq is as follows.
6352 *
6353 * Here bfqq->dispatched > 0 holds, but
6354 * bfq_bfqq_must_idle() returned true. This
6355 * implies that, even if no request arrives
6356 * for bfqq before bfqq->dispatched reaches 0,
6357 * bfqq will, however, not be expired on the
6358 * completion event that causes bfqq->dispatch
6359 * to reach zero. In contrast, on this event,
6360 * bfqq will start enjoying device idling
6361 * (I/O-dispatch plugging).
6362 *
6363 * But, if we expired bfqq here, bfqq would
6364 * not have the chance to enjoy device idling
6365 * when bfqq->dispatched finally reaches
6366 * zero. This would expose bfqq to violation
6367 * of its reserved service guarantees.
6368 */
6369 return;
6370 } else if (bfq_may_expire_for_budg_timeout(bfqq))
6371 bfq_bfqq_expire(bfqd, bfqq, false,
6372 BFQQE_BUDGET_TIMEOUT);
6373 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
6374 (bfqq->dispatched == 0 ||
6375 !bfq_better_to_idle(bfqq)))
6376 bfq_bfqq_expire(bfqd, bfqq, false,
6377 BFQQE_NO_MORE_REQUESTS);
6378 }
6379
6380 if (!bfqd->rq_in_driver)
6381 bfq_schedule_dispatch(bfqd);
6382 }
6383
6384 /*
6385 * The processes associated with bfqq may happen to generate their
6386 * cumulative I/O at a lower rate than the rate at which the device
6387 * could serve the same I/O. This is rather probable, e.g., if only
6388 * one process is associated with bfqq and the device is an SSD. It
6389 * results in bfqq becoming often empty while in service. In this
6390 * respect, if BFQ is allowed to switch to another queue when bfqq
6391 * remains empty, then the device goes on being fed with I/O requests,
6392 * and the throughput is not affected. In contrast, if BFQ is not
6393 * allowed to switch to another queue---because bfqq is sync and
6394 * I/O-dispatch needs to be plugged while bfqq is temporarily
6395 * empty---then, during the service of bfqq, there will be frequent
6396 * "service holes", i.e., time intervals during which bfqq gets empty
6397 * and the device can only consume the I/O already queued in its
6398 * hardware queues. During service holes, the device may even get to
6399 * remaining idle. In the end, during the service of bfqq, the device
6400 * is driven at a lower speed than the one it can reach with the kind
6401 * of I/O flowing through bfqq.
6402 *
6403 * To counter this loss of throughput, BFQ implements a "request
6404 * injection mechanism", which tries to fill the above service holes
6405 * with I/O requests taken from other queues. The hard part in this
6406 * mechanism is finding the right amount of I/O to inject, so as to
6407 * both boost throughput and not break bfqq's bandwidth and latency
6408 * guarantees. In this respect, the mechanism maintains a per-queue
6409 * inject limit, computed as below. While bfqq is empty, the injection
6410 * mechanism dispatches extra I/O requests only until the total number
6411 * of I/O requests in flight---i.e., already dispatched but not yet
6412 * completed---remains lower than this limit.
6413 *
6414 * A first definition comes in handy to introduce the algorithm by
6415 * which the inject limit is computed. We define as first request for
6416 * bfqq, an I/O request for bfqq that arrives while bfqq is in
6417 * service, and causes bfqq to switch from empty to non-empty. The
6418 * algorithm updates the limit as a function of the effect of
6419 * injection on the service times of only the first requests of
6420 * bfqq. The reason for this restriction is that these are the
6421 * requests whose service time is affected most, because they are the
6422 * first to arrive after injection possibly occurred.
6423 *
6424 * To evaluate the effect of injection, the algorithm measures the
6425 * "total service time" of first requests. We define as total service
6426 * time of an I/O request, the time that elapses since when the
6427 * request is enqueued into bfqq, to when it is completed. This
6428 * quantity allows the whole effect of injection to be measured. It is
6429 * easy to see why. Suppose that some requests of other queues are
6430 * actually injected while bfqq is empty, and that a new request R
6431 * then arrives for bfqq. If the device does start to serve all or
6432 * part of the injected requests during the service hole, then,
6433 * because of this extra service, it may delay the next invocation of
6434 * the dispatch hook of BFQ. Then, even after R gets eventually
6435 * dispatched, the device may delay the actual service of R if it is
6436 * still busy serving the extra requests, or if it decides to serve,
6437 * before R, some extra request still present in its queues. As a
6438 * conclusion, the cumulative extra delay caused by injection can be
6439 * easily evaluated by just comparing the total service time of first
6440 * requests with and without injection.
6441 *
6442 * The limit-update algorithm works as follows. On the arrival of a
6443 * first request of bfqq, the algorithm measures the total time of the
6444 * request only if one of the three cases below holds, and, for each
6445 * case, it updates the limit as described below:
6446 *
6447 * (1) If there is no in-flight request. This gives a baseline for the
6448 * total service time of the requests of bfqq. If the baseline has
6449 * not been computed yet, then, after computing it, the limit is
6450 * set to 1, to start boosting throughput, and to prepare the
6451 * ground for the next case. If the baseline has already been
6452 * computed, then it is updated, in case it results to be lower
6453 * than the previous value.
6454 *
6455 * (2) If the limit is higher than 0 and there are in-flight
6456 * requests. By comparing the total service time in this case with
6457 * the above baseline, it is possible to know at which extent the
6458 * current value of the limit is inflating the total service
6459 * time. If the inflation is below a certain threshold, then bfqq
6460 * is assumed to be suffering from no perceivable loss of its
6461 * service guarantees, and the limit is even tentatively
6462 * increased. If the inflation is above the threshold, then the
6463 * limit is decreased. Due to the lack of any hysteresis, this
6464 * logic makes the limit oscillate even in steady workload
6465 * conditions. Yet we opted for it, because it is fast in reaching
6466 * the best value for the limit, as a function of the current I/O
6467 * workload. To reduce oscillations, this step is disabled for a
6468 * short time interval after the limit happens to be decreased.
6469 *
6470 * (3) Periodically, after resetting the limit, to make sure that the
6471 * limit eventually drops in case the workload changes. This is
6472 * needed because, after the limit has gone safely up for a
6473 * certain workload, it is impossible to guess whether the
6474 * baseline total service time may have changed, without measuring
6475 * it again without injection. A more effective version of this
6476 * step might be to just sample the baseline, by interrupting
6477 * injection only once, and then to reset/lower the limit only if
6478 * the total service time with the current limit does happen to be
6479 * too large.
6480 *
6481 * More details on each step are provided in the comments on the
6482 * pieces of code that implement these steps: the branch handling the
6483 * transition from empty to non empty in bfq_add_request(), the branch
6484 * handling injection in bfq_select_queue(), and the function
6485 * bfq_choose_bfqq_for_injection(). These comments also explain some
6486 * exceptions, made by the injection mechanism in some special cases.
6487 */
bfq_update_inject_limit(struct bfq_data * bfqd,struct bfq_queue * bfqq)6488 static void bfq_update_inject_limit(struct bfq_data *bfqd,
6489 struct bfq_queue *bfqq)
6490 {
6491 u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns;
6492 unsigned int old_limit = bfqq->inject_limit;
6493
6494 if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
6495 u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
6496
6497 if (tot_time_ns >= threshold && old_limit > 0) {
6498 bfqq->inject_limit--;
6499 bfqq->decrease_time_jif = jiffies;
6500 } else if (tot_time_ns < threshold &&
6501 old_limit <= bfqd->max_rq_in_driver)
6502 bfqq->inject_limit++;
6503 }
6504
6505 /*
6506 * Either we still have to compute the base value for the
6507 * total service time, and there seem to be the right
6508 * conditions to do it, or we can lower the last base value
6509 * computed.
6510 *
6511 * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
6512 * request in flight, because this function is in the code
6513 * path that handles the completion of a request of bfqq, and,
6514 * in particular, this function is executed before
6515 * bfqd->rq_in_driver is decremented in such a code path.
6516 */
6517 if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) ||
6518 tot_time_ns < bfqq->last_serv_time_ns) {
6519 if (bfqq->last_serv_time_ns == 0) {
6520 /*
6521 * Now we certainly have a base value: make sure we
6522 * start trying injection.
6523 */
6524 bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
6525 }
6526 bfqq->last_serv_time_ns = tot_time_ns;
6527 } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
6528 /*
6529 * No I/O injected and no request still in service in
6530 * the drive: these are the exact conditions for
6531 * computing the base value of the total service time
6532 * for bfqq. So let's update this value, because it is
6533 * rather variable. For example, it varies if the size
6534 * or the spatial locality of the I/O requests in bfqq
6535 * change.
6536 */
6537 bfqq->last_serv_time_ns = tot_time_ns;
6538
6539
6540 /* update complete, not waiting for any request completion any longer */
6541 bfqd->waited_rq = NULL;
6542 bfqd->rqs_injected = false;
6543 }
6544
6545 /*
6546 * Handle either a requeue or a finish for rq. The things to do are
6547 * the same in both cases: all references to rq are to be dropped. In
6548 * particular, rq is considered completed from the point of view of
6549 * the scheduler.
6550 */
bfq_finish_requeue_request(struct request * rq)6551 static void bfq_finish_requeue_request(struct request *rq)
6552 {
6553 struct bfq_queue *bfqq = RQ_BFQQ(rq);
6554 struct bfq_data *bfqd;
6555 unsigned long flags;
6556
6557 /*
6558 * rq either is not associated with any icq, or is an already
6559 * requeued request that has not (yet) been re-inserted into
6560 * a bfq_queue.
6561 */
6562 if (!rq->elv.icq || !bfqq)
6563 return;
6564
6565 bfqd = bfqq->bfqd;
6566
6567 if (rq->rq_flags & RQF_STARTED)
6568 bfqg_stats_update_completion(bfqq_group(bfqq),
6569 rq->start_time_ns,
6570 rq->io_start_time_ns,
6571 rq->cmd_flags);
6572
6573 spin_lock_irqsave(&bfqd->lock, flags);
6574 if (likely(rq->rq_flags & RQF_STARTED)) {
6575 if (rq == bfqd->waited_rq)
6576 bfq_update_inject_limit(bfqd, bfqq);
6577
6578 bfq_completed_request(bfqq, bfqd);
6579 }
6580 bfqq_request_freed(bfqq);
6581 bfq_put_queue(bfqq);
6582 RQ_BIC(rq)->requests--;
6583 spin_unlock_irqrestore(&bfqd->lock, flags);
6584
6585 /*
6586 * Reset private fields. In case of a requeue, this allows
6587 * this function to correctly do nothing if it is spuriously
6588 * invoked again on this same request (see the check at the
6589 * beginning of the function). Probably, a better general
6590 * design would be to prevent blk-mq from invoking the requeue
6591 * or finish hooks of an elevator, for a request that is not
6592 * referred by that elevator.
6593 *
6594 * Resetting the following fields would break the
6595 * request-insertion logic if rq is re-inserted into a bfq
6596 * internal queue, without a re-preparation. Here we assume
6597 * that re-insertions of requeued requests, without
6598 * re-preparation, can happen only for pass_through or at_head
6599 * requests (which are not re-inserted into bfq internal
6600 * queues).
6601 */
6602 rq->elv.priv[0] = NULL;
6603 rq->elv.priv[1] = NULL;
6604 }
6605
bfq_finish_request(struct request * rq)6606 static void bfq_finish_request(struct request *rq)
6607 {
6608 bfq_finish_requeue_request(rq);
6609
6610 if (rq->elv.icq) {
6611 put_io_context(rq->elv.icq->ioc);
6612 rq->elv.icq = NULL;
6613 }
6614 }
6615
6616 /*
6617 * Removes the association between the current task and bfqq, assuming
6618 * that bic points to the bfq iocontext of the task.
6619 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
6620 * was the last process referring to that bfqq.
6621 */
6622 static struct bfq_queue *
bfq_split_bfqq(struct bfq_io_cq * bic,struct bfq_queue * bfqq)6623 bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
6624 {
6625 bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
6626
6627 if (bfqq_process_refs(bfqq) == 1) {
6628 bfqq->pid = current->pid;
6629 bfq_clear_bfqq_coop(bfqq);
6630 bfq_clear_bfqq_split_coop(bfqq);
6631 return bfqq;
6632 }
6633
6634 bic_set_bfqq(bic, NULL, true);
6635
6636 bfq_put_cooperator(bfqq);
6637
6638 bfq_release_process_ref(bfqq->bfqd, bfqq);
6639 return NULL;
6640 }
6641
bfq_get_bfqq_handle_split(struct bfq_data * bfqd,struct bfq_io_cq * bic,struct bio * bio,bool split,bool is_sync,bool * new_queue)6642 static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
6643 struct bfq_io_cq *bic,
6644 struct bio *bio,
6645 bool split, bool is_sync,
6646 bool *new_queue)
6647 {
6648 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
6649
6650 if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6651 return bfqq;
6652
6653 if (new_queue)
6654 *new_queue = true;
6655
6656 if (bfqq)
6657 bfq_put_queue(bfqq);
6658 bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, split);
6659
6660 bic_set_bfqq(bic, bfqq, is_sync);
6661 if (split && is_sync) {
6662 if ((bic->was_in_burst_list && bfqd->large_burst) ||
6663 bic->saved_in_large_burst)
6664 bfq_mark_bfqq_in_large_burst(bfqq);
6665 else {
6666 bfq_clear_bfqq_in_large_burst(bfqq);
6667 if (bic->was_in_burst_list)
6668 /*
6669 * If bfqq was in the current
6670 * burst list before being
6671 * merged, then we have to add
6672 * it back. And we do not need
6673 * to increase burst_size, as
6674 * we did not decrement
6675 * burst_size when we removed
6676 * bfqq from the burst list as
6677 * a consequence of a merge
6678 * (see comments in
6679 * bfq_put_queue). In this
6680 * respect, it would be rather
6681 * costly to know whether the
6682 * current burst list is still
6683 * the same burst list from
6684 * which bfqq was removed on
6685 * the merge. To avoid this
6686 * cost, if bfqq was in a
6687 * burst list, then we add
6688 * bfqq to the current burst
6689 * list without any further
6690 * check. This can cause
6691 * inappropriate insertions,
6692 * but rarely enough to not
6693 * harm the detection of large
6694 * bursts significantly.
6695 */
6696 hlist_add_head(&bfqq->burst_list_node,
6697 &bfqd->burst_list);
6698 }
6699 bfqq->split_time = jiffies;
6700 }
6701
6702 return bfqq;
6703 }
6704
6705 /*
6706 * Only reset private fields. The actual request preparation will be
6707 * performed by bfq_init_rq, when rq is either inserted or merged. See
6708 * comments on bfq_init_rq for the reason behind this delayed
6709 * preparation.
6710 */
bfq_prepare_request(struct request * rq)6711 static void bfq_prepare_request(struct request *rq)
6712 {
6713 rq->elv.icq = ioc_find_get_icq(rq->q);
6714
6715 /*
6716 * Regardless of whether we have an icq attached, we have to
6717 * clear the scheduler pointers, as they might point to
6718 * previously allocated bic/bfqq structs.
6719 */
6720 rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6721 }
6722
6723 /*
6724 * If needed, init rq, allocate bfq data structures associated with
6725 * rq, and increment reference counters in the destination bfq_queue
6726 * for rq. Return the destination bfq_queue for rq, or NULL is rq is
6727 * not associated with any bfq_queue.
6728 *
6729 * This function is invoked by the functions that perform rq insertion
6730 * or merging. One may have expected the above preparation operations
6731 * to be performed in bfq_prepare_request, and not delayed to when rq
6732 * is inserted or merged. The rationale behind this delayed
6733 * preparation is that, after the prepare_request hook is invoked for
6734 * rq, rq may still be transformed into a request with no icq, i.e., a
6735 * request not associated with any queue. No bfq hook is invoked to
6736 * signal this transformation. As a consequence, should these
6737 * preparation operations be performed when the prepare_request hook
6738 * is invoked, and should rq be transformed one moment later, bfq
6739 * would end up in an inconsistent state, because it would have
6740 * incremented some queue counters for an rq destined to
6741 * transformation, without any chance to correctly lower these
6742 * counters back. In contrast, no transformation can still happen for
6743 * rq after rq has been inserted or merged. So, it is safe to execute
6744 * these preparation operations when rq is finally inserted or merged.
6745 */
bfq_init_rq(struct request * rq)6746 static struct bfq_queue *bfq_init_rq(struct request *rq)
6747 {
6748 struct request_queue *q = rq->q;
6749 struct bio *bio = rq->bio;
6750 struct bfq_data *bfqd = q->elevator->elevator_data;
6751 struct bfq_io_cq *bic;
6752 const int is_sync = rq_is_sync(rq);
6753 struct bfq_queue *bfqq;
6754 bool new_queue = false;
6755 bool bfqq_already_existing = false, split = false;
6756
6757 if (unlikely(!rq->elv.icq))
6758 return NULL;
6759
6760 /*
6761 * Assuming that elv.priv[1] is set only if everything is set
6762 * for this rq. This holds true, because this function is
6763 * invoked only for insertion or merging, and, after such
6764 * events, a request cannot be manipulated any longer before
6765 * being removed from bfq.
6766 */
6767 if (rq->elv.priv[1])
6768 return rq->elv.priv[1];
6769
6770 bic = icq_to_bic(rq->elv.icq);
6771
6772 bfq_check_ioprio_change(bic, bio);
6773
6774 bfq_bic_update_cgroup(bic, bio);
6775
6776 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
6777 &new_queue);
6778
6779 if (likely(!new_queue)) {
6780 /* If the queue was seeky for too long, break it apart. */
6781 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
6782 !bic->stably_merged) {
6783 struct bfq_queue *old_bfqq = bfqq;
6784
6785 /* Update bic before losing reference to bfqq */
6786 if (bfq_bfqq_in_large_burst(bfqq))
6787 bic->saved_in_large_burst = true;
6788
6789 bfqq = bfq_split_bfqq(bic, bfqq);
6790 split = true;
6791
6792 if (!bfqq) {
6793 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6794 true, is_sync,
6795 NULL);
6796 if (unlikely(bfqq == &bfqd->oom_bfqq))
6797 bfqq_already_existing = true;
6798 } else
6799 bfqq_already_existing = true;
6800
6801 if (!bfqq_already_existing) {
6802 bfqq->waker_bfqq = old_bfqq->waker_bfqq;
6803 bfqq->tentative_waker_bfqq = NULL;
6804
6805 /*
6806 * If the waker queue disappears, then
6807 * new_bfqq->waker_bfqq must be
6808 * reset. So insert new_bfqq into the
6809 * woken_list of the waker. See
6810 * bfq_check_waker for details.
6811 */
6812 if (bfqq->waker_bfqq)
6813 hlist_add_head(&bfqq->woken_list_node,
6814 &bfqq->waker_bfqq->woken_list);
6815 }
6816 }
6817 }
6818
6819 bfqq_request_allocated(bfqq);
6820 bfqq->ref++;
6821 bic->requests++;
6822 bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6823 rq, bfqq, bfqq->ref);
6824
6825 rq->elv.priv[0] = bic;
6826 rq->elv.priv[1] = bfqq;
6827
6828 /*
6829 * If a bfq_queue has only one process reference, it is owned
6830 * by only this bic: we can then set bfqq->bic = bic. in
6831 * addition, if the queue has also just been split, we have to
6832 * resume its state.
6833 */
6834 if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6835 bfqq->bic = bic;
6836 if (split) {
6837 /*
6838 * The queue has just been split from a shared
6839 * queue: restore the idle window and the
6840 * possible weight raising period.
6841 */
6842 bfq_bfqq_resume_state(bfqq, bfqd, bic,
6843 bfqq_already_existing);
6844 }
6845 }
6846
6847 /*
6848 * Consider bfqq as possibly belonging to a burst of newly
6849 * created queues only if:
6850 * 1) A burst is actually happening (bfqd->burst_size > 0)
6851 * or
6852 * 2) There is no other active queue. In fact, if, in
6853 * contrast, there are active queues not belonging to the
6854 * possible burst bfqq may belong to, then there is no gain
6855 * in considering bfqq as belonging to a burst, and
6856 * therefore in not weight-raising bfqq. See comments on
6857 * bfq_handle_burst().
6858 *
6859 * This filtering also helps eliminating false positives,
6860 * occurring when bfqq does not belong to an actual large
6861 * burst, but some background task (e.g., a service) happens
6862 * to trigger the creation of new queues very close to when
6863 * bfqq and its possible companion queues are created. See
6864 * comments on bfq_handle_burst() for further details also on
6865 * this issue.
6866 */
6867 if (unlikely(bfq_bfqq_just_created(bfqq) &&
6868 (bfqd->burst_size > 0 ||
6869 bfq_tot_busy_queues(bfqd) == 0)))
6870 bfq_handle_burst(bfqd, bfqq);
6871
6872 return bfqq;
6873 }
6874
6875 static void
bfq_idle_slice_timer_body(struct bfq_data * bfqd,struct bfq_queue * bfqq)6876 bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6877 {
6878 enum bfqq_expiration reason;
6879 unsigned long flags;
6880
6881 spin_lock_irqsave(&bfqd->lock, flags);
6882
6883 /*
6884 * Considering that bfqq may be in race, we should firstly check
6885 * whether bfqq is in service before doing something on it. If
6886 * the bfqq in race is not in service, it has already been expired
6887 * through __bfq_bfqq_expire func and its wait_request flags has
6888 * been cleared in __bfq_bfqd_reset_in_service func.
6889 */
6890 if (bfqq != bfqd->in_service_queue) {
6891 spin_unlock_irqrestore(&bfqd->lock, flags);
6892 return;
6893 }
6894
6895 bfq_clear_bfqq_wait_request(bfqq);
6896
6897 if (bfq_bfqq_budget_timeout(bfqq))
6898 /*
6899 * Also here the queue can be safely expired
6900 * for budget timeout without wasting
6901 * guarantees
6902 */
6903 reason = BFQQE_BUDGET_TIMEOUT;
6904 else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
6905 /*
6906 * The queue may not be empty upon timer expiration,
6907 * because we may not disable the timer when the
6908 * first request of the in-service queue arrives
6909 * during disk idling.
6910 */
6911 reason = BFQQE_TOO_IDLE;
6912 else
6913 goto schedule_dispatch;
6914
6915 bfq_bfqq_expire(bfqd, bfqq, true, reason);
6916
6917 schedule_dispatch:
6918 bfq_schedule_dispatch(bfqd);
6919 spin_unlock_irqrestore(&bfqd->lock, flags);
6920 }
6921
6922 /*
6923 * Handler of the expiration of the timer running if the in-service queue
6924 * is idling inside its time slice.
6925 */
bfq_idle_slice_timer(struct hrtimer * timer)6926 static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
6927 {
6928 struct bfq_data *bfqd = container_of(timer, struct bfq_data,
6929 idle_slice_timer);
6930 struct bfq_queue *bfqq = bfqd->in_service_queue;
6931
6932 /*
6933 * Theoretical race here: the in-service queue can be NULL or
6934 * different from the queue that was idling if a new request
6935 * arrives for the current queue and there is a full dispatch
6936 * cycle that changes the in-service queue. This can hardly
6937 * happen, but in the worst case we just expire a queue too
6938 * early.
6939 */
6940 if (bfqq)
6941 bfq_idle_slice_timer_body(bfqd, bfqq);
6942
6943 return HRTIMER_NORESTART;
6944 }
6945
__bfq_put_async_bfqq(struct bfq_data * bfqd,struct bfq_queue ** bfqq_ptr)6946 static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
6947 struct bfq_queue **bfqq_ptr)
6948 {
6949 struct bfq_queue *bfqq = *bfqq_ptr;
6950
6951 bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
6952 if (bfqq) {
6953 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
6954
6955 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
6956 bfqq, bfqq->ref);
6957 bfq_put_queue(bfqq);
6958 *bfqq_ptr = NULL;
6959 }
6960 }
6961
6962 /*
6963 * Release all the bfqg references to its async queues. If we are
6964 * deallocating the group these queues may still contain requests, so
6965 * we reparent them to the root cgroup (i.e., the only one that will
6966 * exist for sure until all the requests on a device are gone).
6967 */
bfq_put_async_queues(struct bfq_data * bfqd,struct bfq_group * bfqg)6968 void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
6969 {
6970 int i, j;
6971
6972 for (i = 0; i < 2; i++)
6973 for (j = 0; j < IOPRIO_NR_LEVELS; j++)
6974 __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
6975
6976 __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
6977 }
6978
6979 /*
6980 * See the comments on bfq_limit_depth for the purpose of
6981 * the depths set in the function. Return minimum shallow depth we'll use.
6982 */
bfq_update_depths(struct bfq_data * bfqd,struct sbitmap_queue * bt)6983 static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
6984 {
6985 unsigned int depth = 1U << bt->sb.shift;
6986
6987 bfqd->full_depth_shift = bt->sb.shift;
6988 /*
6989 * In-word depths if no bfq_queue is being weight-raised:
6990 * leaving 25% of tags only for sync reads.
6991 *
6992 * In next formulas, right-shift the value
6993 * (1U<<bt->sb.shift), instead of computing directly
6994 * (1U<<(bt->sb.shift - something)), to be robust against
6995 * any possible value of bt->sb.shift, without having to
6996 * limit 'something'.
6997 */
6998 /* no more than 50% of tags for async I/O */
6999 bfqd->word_depths[0][0] = max(depth >> 1, 1U);
7000 /*
7001 * no more than 75% of tags for sync writes (25% extra tags
7002 * w.r.t. async I/O, to prevent async I/O from starving sync
7003 * writes)
7004 */
7005 bfqd->word_depths[0][1] = max((depth * 3) >> 2, 1U);
7006
7007 /*
7008 * In-word depths in case some bfq_queue is being weight-
7009 * raised: leaving ~63% of tags for sync reads. This is the
7010 * highest percentage for which, in our tests, application
7011 * start-up times didn't suffer from any regression due to tag
7012 * shortage.
7013 */
7014 /* no more than ~18% of tags for async I/O */
7015 bfqd->word_depths[1][0] = max((depth * 3) >> 4, 1U);
7016 /* no more than ~37% of tags for sync writes (~20% extra tags) */
7017 bfqd->word_depths[1][1] = max((depth * 6) >> 4, 1U);
7018 }
7019
bfq_depth_updated(struct blk_mq_hw_ctx * hctx)7020 static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
7021 {
7022 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
7023 struct blk_mq_tags *tags = hctx->sched_tags;
7024
7025 bfq_update_depths(bfqd, &tags->bitmap_tags);
7026 sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, 1);
7027 }
7028
bfq_init_hctx(struct blk_mq_hw_ctx * hctx,unsigned int index)7029 static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
7030 {
7031 bfq_depth_updated(hctx);
7032 return 0;
7033 }
7034
bfq_exit_queue(struct elevator_queue * e)7035 static void bfq_exit_queue(struct elevator_queue *e)
7036 {
7037 struct bfq_data *bfqd = e->elevator_data;
7038 struct bfq_queue *bfqq, *n;
7039
7040 hrtimer_cancel(&bfqd->idle_slice_timer);
7041
7042 spin_lock_irq(&bfqd->lock);
7043 list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
7044 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
7045 spin_unlock_irq(&bfqd->lock);
7046
7047 hrtimer_cancel(&bfqd->idle_slice_timer);
7048
7049 /* release oom-queue reference to root group */
7050 bfqg_and_blkg_put(bfqd->root_group);
7051
7052 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7053 blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
7054 #else
7055 spin_lock_irq(&bfqd->lock);
7056 bfq_put_async_queues(bfqd, bfqd->root_group);
7057 kfree(bfqd->root_group);
7058 spin_unlock_irq(&bfqd->lock);
7059 #endif
7060
7061 blk_stat_disable_accounting(bfqd->queue);
7062 wbt_enable_default(bfqd->queue);
7063
7064 kfree(bfqd);
7065 }
7066
bfq_init_root_group(struct bfq_group * root_group,struct bfq_data * bfqd)7067 static void bfq_init_root_group(struct bfq_group *root_group,
7068 struct bfq_data *bfqd)
7069 {
7070 int i;
7071
7072 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7073 root_group->entity.parent = NULL;
7074 root_group->my_entity = NULL;
7075 root_group->bfqd = bfqd;
7076 #endif
7077 root_group->rq_pos_tree = RB_ROOT;
7078 for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
7079 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
7080 root_group->sched_data.bfq_class_idle_last_service = jiffies;
7081 }
7082
bfq_init_queue(struct request_queue * q,struct elevator_type * e)7083 static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
7084 {
7085 struct bfq_data *bfqd;
7086 struct elevator_queue *eq;
7087
7088 eq = elevator_alloc(q, e);
7089 if (!eq)
7090 return -ENOMEM;
7091
7092 bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
7093 if (!bfqd) {
7094 kobject_put(&eq->kobj);
7095 return -ENOMEM;
7096 }
7097 eq->elevator_data = bfqd;
7098
7099 spin_lock_irq(&q->queue_lock);
7100 q->elevator = eq;
7101 spin_unlock_irq(&q->queue_lock);
7102
7103 /*
7104 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
7105 * Grab a permanent reference to it, so that the normal code flow
7106 * will not attempt to free it.
7107 */
7108 bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
7109 bfqd->oom_bfqq.ref++;
7110 bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
7111 bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
7112 bfqd->oom_bfqq.entity.new_weight =
7113 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
7114
7115 /* oom_bfqq does not participate to bursts */
7116 bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
7117
7118 /*
7119 * Trigger weight initialization, according to ioprio, at the
7120 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
7121 * class won't be changed any more.
7122 */
7123 bfqd->oom_bfqq.entity.prio_changed = 1;
7124
7125 bfqd->queue = q;
7126
7127 INIT_LIST_HEAD(&bfqd->dispatch);
7128
7129 hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
7130 HRTIMER_MODE_REL);
7131 bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
7132
7133 bfqd->queue_weights_tree = RB_ROOT_CACHED;
7134 bfqd->num_groups_with_pending_reqs = 0;
7135
7136 INIT_LIST_HEAD(&bfqd->active_list);
7137 INIT_LIST_HEAD(&bfqd->idle_list);
7138 INIT_HLIST_HEAD(&bfqd->burst_list);
7139
7140 bfqd->hw_tag = -1;
7141 bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
7142
7143 bfqd->bfq_max_budget = bfq_default_max_budget;
7144
7145 bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
7146 bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
7147 bfqd->bfq_back_max = bfq_back_max;
7148 bfqd->bfq_back_penalty = bfq_back_penalty;
7149 bfqd->bfq_slice_idle = bfq_slice_idle;
7150 bfqd->bfq_timeout = bfq_timeout;
7151
7152 bfqd->bfq_large_burst_thresh = 8;
7153 bfqd->bfq_burst_interval = msecs_to_jiffies(180);
7154
7155 bfqd->low_latency = true;
7156
7157 /*
7158 * Trade-off between responsiveness and fairness.
7159 */
7160 bfqd->bfq_wr_coeff = 30;
7161 bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
7162 bfqd->bfq_wr_max_time = 0;
7163 bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
7164 bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
7165 bfqd->bfq_wr_max_softrt_rate = 7000; /*
7166 * Approximate rate required
7167 * to playback or record a
7168 * high-definition compressed
7169 * video.
7170 */
7171 bfqd->wr_busy_queues = 0;
7172
7173 /*
7174 * Begin by assuming, optimistically, that the device peak
7175 * rate is equal to 2/3 of the highest reference rate.
7176 */
7177 bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
7178 ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
7179 bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
7180
7181 spin_lock_init(&bfqd->lock);
7182
7183 /*
7184 * The invocation of the next bfq_create_group_hierarchy
7185 * function is the head of a chain of function calls
7186 * (bfq_create_group_hierarchy->blkcg_activate_policy->
7187 * blk_mq_freeze_queue) that may lead to the invocation of the
7188 * has_work hook function. For this reason,
7189 * bfq_create_group_hierarchy is invoked only after all
7190 * scheduler data has been initialized, apart from the fields
7191 * that can be initialized only after invoking
7192 * bfq_create_group_hierarchy. This, in particular, enables
7193 * has_work to correctly return false. Of course, to avoid
7194 * other inconsistencies, the blk-mq stack must then refrain
7195 * from invoking further scheduler hooks before this init
7196 * function is finished.
7197 */
7198 bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
7199 if (!bfqd->root_group)
7200 goto out_free;
7201 bfq_init_root_group(bfqd->root_group, bfqd);
7202 bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
7203
7204 /* We dispatch from request queue wide instead of hw queue */
7205 blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
7206
7207 wbt_disable_default(q);
7208 blk_stat_enable_accounting(q);
7209
7210 return 0;
7211
7212 out_free:
7213 kfree(bfqd);
7214 kobject_put(&eq->kobj);
7215 return -ENOMEM;
7216 }
7217
bfq_slab_kill(void)7218 static void bfq_slab_kill(void)
7219 {
7220 kmem_cache_destroy(bfq_pool);
7221 }
7222
bfq_slab_setup(void)7223 static int __init bfq_slab_setup(void)
7224 {
7225 bfq_pool = KMEM_CACHE(bfq_queue, 0);
7226 if (!bfq_pool)
7227 return -ENOMEM;
7228 return 0;
7229 }
7230
bfq_var_show(unsigned int var,char * page)7231 static ssize_t bfq_var_show(unsigned int var, char *page)
7232 {
7233 return sprintf(page, "%u\n", var);
7234 }
7235
bfq_var_store(unsigned long * var,const char * page)7236 static int bfq_var_store(unsigned long *var, const char *page)
7237 {
7238 unsigned long new_val;
7239 int ret = kstrtoul(page, 10, &new_val);
7240
7241 if (ret)
7242 return ret;
7243 *var = new_val;
7244 return 0;
7245 }
7246
7247 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
7248 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7249 { \
7250 struct bfq_data *bfqd = e->elevator_data; \
7251 u64 __data = __VAR; \
7252 if (__CONV == 1) \
7253 __data = jiffies_to_msecs(__data); \
7254 else if (__CONV == 2) \
7255 __data = div_u64(__data, NSEC_PER_MSEC); \
7256 return bfq_var_show(__data, (page)); \
7257 }
7258 SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
7259 SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
7260 SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
7261 SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
7262 SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
7263 SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
7264 SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
7265 SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
7266 SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
7267 #undef SHOW_FUNCTION
7268
7269 #define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
7270 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7271 { \
7272 struct bfq_data *bfqd = e->elevator_data; \
7273 u64 __data = __VAR; \
7274 __data = div_u64(__data, NSEC_PER_USEC); \
7275 return bfq_var_show(__data, (page)); \
7276 }
7277 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
7278 #undef USEC_SHOW_FUNCTION
7279
7280 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
7281 static ssize_t \
7282 __FUNC(struct elevator_queue *e, const char *page, size_t count) \
7283 { \
7284 struct bfq_data *bfqd = e->elevator_data; \
7285 unsigned long __data, __min = (MIN), __max = (MAX); \
7286 int ret; \
7287 \
7288 ret = bfq_var_store(&__data, (page)); \
7289 if (ret) \
7290 return ret; \
7291 if (__data < __min) \
7292 __data = __min; \
7293 else if (__data > __max) \
7294 __data = __max; \
7295 if (__CONV == 1) \
7296 *(__PTR) = msecs_to_jiffies(__data); \
7297 else if (__CONV == 2) \
7298 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
7299 else \
7300 *(__PTR) = __data; \
7301 return count; \
7302 }
7303 STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
7304 INT_MAX, 2);
7305 STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
7306 INT_MAX, 2);
7307 STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
7308 STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
7309 INT_MAX, 0);
7310 STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
7311 #undef STORE_FUNCTION
7312
7313 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
7314 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
7315 { \
7316 struct bfq_data *bfqd = e->elevator_data; \
7317 unsigned long __data, __min = (MIN), __max = (MAX); \
7318 int ret; \
7319 \
7320 ret = bfq_var_store(&__data, (page)); \
7321 if (ret) \
7322 return ret; \
7323 if (__data < __min) \
7324 __data = __min; \
7325 else if (__data > __max) \
7326 __data = __max; \
7327 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
7328 return count; \
7329 }
7330 USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
7331 UINT_MAX);
7332 #undef USEC_STORE_FUNCTION
7333
bfq_max_budget_store(struct elevator_queue * e,const char * page,size_t count)7334 static ssize_t bfq_max_budget_store(struct elevator_queue *e,
7335 const char *page, size_t count)
7336 {
7337 struct bfq_data *bfqd = e->elevator_data;
7338 unsigned long __data;
7339 int ret;
7340
7341 ret = bfq_var_store(&__data, (page));
7342 if (ret)
7343 return ret;
7344
7345 if (__data == 0)
7346 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7347 else {
7348 if (__data > INT_MAX)
7349 __data = INT_MAX;
7350 bfqd->bfq_max_budget = __data;
7351 }
7352
7353 bfqd->bfq_user_max_budget = __data;
7354
7355 return count;
7356 }
7357
7358 /*
7359 * Leaving this name to preserve name compatibility with cfq
7360 * parameters, but this timeout is used for both sync and async.
7361 */
bfq_timeout_sync_store(struct elevator_queue * e,const char * page,size_t count)7362 static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
7363 const char *page, size_t count)
7364 {
7365 struct bfq_data *bfqd = e->elevator_data;
7366 unsigned long __data;
7367 int ret;
7368
7369 ret = bfq_var_store(&__data, (page));
7370 if (ret)
7371 return ret;
7372
7373 if (__data < 1)
7374 __data = 1;
7375 else if (__data > INT_MAX)
7376 __data = INT_MAX;
7377
7378 bfqd->bfq_timeout = msecs_to_jiffies(__data);
7379 if (bfqd->bfq_user_max_budget == 0)
7380 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7381
7382 return count;
7383 }
7384
bfq_strict_guarantees_store(struct elevator_queue * e,const char * page,size_t count)7385 static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
7386 const char *page, size_t count)
7387 {
7388 struct bfq_data *bfqd = e->elevator_data;
7389 unsigned long __data;
7390 int ret;
7391
7392 ret = bfq_var_store(&__data, (page));
7393 if (ret)
7394 return ret;
7395
7396 if (__data > 1)
7397 __data = 1;
7398 if (!bfqd->strict_guarantees && __data == 1
7399 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
7400 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
7401
7402 bfqd->strict_guarantees = __data;
7403
7404 return count;
7405 }
7406
bfq_low_latency_store(struct elevator_queue * e,const char * page,size_t count)7407 static ssize_t bfq_low_latency_store(struct elevator_queue *e,
7408 const char *page, size_t count)
7409 {
7410 struct bfq_data *bfqd = e->elevator_data;
7411 unsigned long __data;
7412 int ret;
7413
7414 ret = bfq_var_store(&__data, (page));
7415 if (ret)
7416 return ret;
7417
7418 if (__data > 1)
7419 __data = 1;
7420 if (__data == 0 && bfqd->low_latency != 0)
7421 bfq_end_wr(bfqd);
7422 bfqd->low_latency = __data;
7423
7424 return count;
7425 }
7426
7427 #define BFQ_ATTR(name) \
7428 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
7429
7430 static struct elv_fs_entry bfq_attrs[] = {
7431 BFQ_ATTR(fifo_expire_sync),
7432 BFQ_ATTR(fifo_expire_async),
7433 BFQ_ATTR(back_seek_max),
7434 BFQ_ATTR(back_seek_penalty),
7435 BFQ_ATTR(slice_idle),
7436 BFQ_ATTR(slice_idle_us),
7437 BFQ_ATTR(max_budget),
7438 BFQ_ATTR(timeout_sync),
7439 BFQ_ATTR(strict_guarantees),
7440 BFQ_ATTR(low_latency),
7441 __ATTR_NULL
7442 };
7443
7444 static struct elevator_type iosched_bfq_mq = {
7445 .ops = {
7446 .limit_depth = bfq_limit_depth,
7447 .prepare_request = bfq_prepare_request,
7448 .requeue_request = bfq_finish_requeue_request,
7449 .finish_request = bfq_finish_request,
7450 .exit_icq = bfq_exit_icq,
7451 .insert_requests = bfq_insert_requests,
7452 .dispatch_request = bfq_dispatch_request,
7453 .next_request = elv_rb_latter_request,
7454 .former_request = elv_rb_former_request,
7455 .allow_merge = bfq_allow_bio_merge,
7456 .bio_merge = bfq_bio_merge,
7457 .request_merge = bfq_request_merge,
7458 .requests_merged = bfq_requests_merged,
7459 .request_merged = bfq_request_merged,
7460 .has_work = bfq_has_work,
7461 .depth_updated = bfq_depth_updated,
7462 .init_hctx = bfq_init_hctx,
7463 .init_sched = bfq_init_queue,
7464 .exit_sched = bfq_exit_queue,
7465 },
7466
7467 .icq_size = sizeof(struct bfq_io_cq),
7468 .icq_align = __alignof__(struct bfq_io_cq),
7469 .elevator_attrs = bfq_attrs,
7470 .elevator_name = "bfq",
7471 .elevator_owner = THIS_MODULE,
7472 };
7473 MODULE_ALIAS("bfq-iosched");
7474
bfq_init(void)7475 static int __init bfq_init(void)
7476 {
7477 int ret;
7478
7479 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7480 ret = blkcg_policy_register(&blkcg_policy_bfq);
7481 if (ret)
7482 return ret;
7483 #endif
7484
7485 ret = -ENOMEM;
7486 if (bfq_slab_setup())
7487 goto err_pol_unreg;
7488
7489 /*
7490 * Times to load large popular applications for the typical
7491 * systems installed on the reference devices (see the
7492 * comments before the definition of the next
7493 * array). Actually, we use slightly lower values, as the
7494 * estimated peak rate tends to be smaller than the actual
7495 * peak rate. The reason for this last fact is that estimates
7496 * are computed over much shorter time intervals than the long
7497 * intervals typically used for benchmarking. Why? First, to
7498 * adapt more quickly to variations. Second, because an I/O
7499 * scheduler cannot rely on a peak-rate-evaluation workload to
7500 * be run for a long time.
7501 */
7502 ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
7503 ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
7504
7505 ret = elv_register(&iosched_bfq_mq);
7506 if (ret)
7507 goto slab_kill;
7508
7509 return 0;
7510
7511 slab_kill:
7512 bfq_slab_kill();
7513 err_pol_unreg:
7514 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7515 blkcg_policy_unregister(&blkcg_policy_bfq);
7516 #endif
7517 return ret;
7518 }
7519
bfq_exit(void)7520 static void __exit bfq_exit(void)
7521 {
7522 elv_unregister(&iosched_bfq_mq);
7523 #ifdef CONFIG_BFQ_GROUP_IOSCHED
7524 blkcg_policy_unregister(&blkcg_policy_bfq);
7525 #endif
7526 bfq_slab_kill();
7527 }
7528
7529 module_init(bfq_init);
7530 module_exit(bfq_exit);
7531
7532 MODULE_AUTHOR("Paolo Valente");
7533 MODULE_LICENSE("GPL");
7534 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
7535